function Browser(window, document, $log, $sniffer) {
  var self = this,
      rawDocument = document[0],
      location = window.location,
      history = window.history,
      setTimeout = window.setTimeout,
      clearTimeout = window.clearTimeout,
      pendingDeferIds = {};

  self.isMock = false;

  var outstandingRequestCount = 0;
  var outstandingRequestCallbacks = [];

  // TODO(vojta): remove this temporary api
  self.$$completeOutstandingRequest = completeOutstandingRequest;
  self.$$incOutstandingRequestCount = function() { outstandingRequestCount++; };

  /**
   * Executes the `fn` function(supports currying) and decrements the `outstandingRequestCallbacks`
   * counter. If the counter reaches 0, all the `outstandingRequestCallbacks` are executed.
   */
  function completeOutstandingRequest(fn) {
    try {
      fn.apply(null, sliceArgs(arguments, 1));
    } finally {
      outstandingRequestCount--;
      if (outstandingRequestCount === 0) {
        while(outstandingRequestCallbacks.length) {
          try {
            outstandingRequestCallbacks.pop()();
          } catch (e) {
            $log.error(e);
          }
        }
      }
    }
  }

  /**
   * @private
   * Note: this method is used only by scenario runner
   * TODO(vojta): prefix this method with $$ ?
   * @param {function()} callback Function that will be called when no outstanding request
   */
  self.notifyWhenNoOutstandingRequests = function(callback) {
    // force browser to execute all pollFns - this is needed so that cookies and other pollers fire
    // at some deterministic time in respect to the test runner's actions. Leaving things up to the
    // regular poller would result in flaky tests.
    forEach(pollFns, function(pollFn){ pollFn(); });

    if (outstandingRequestCount === 0) {
      callback();
    } else {
      outstandingRequestCallbacks.push(callback);
    }
  };

  //////////////////////////////////////////////////////////////
  // Poll Watcher API
  //////////////////////////////////////////////////////////////
  var pollFns = [],
      pollTimeout;

  /**
   * @name ng.$browser#addPollFn
   * @methodOf ng.$browser
   *
   * @param {function()} fn Poll function to add
   *
   * @description
   * Adds a function to the list of functions that poller periodically executes,
   * and starts polling if not started yet.
   *
   * @returns {function()} the added function
   */
  self.addPollFn = function(fn) {
    if (isUndefined(pollTimeout)) startPoller(100, setTimeout);
    pollFns.push(fn);
    return fn;
  };

  /**
   * @param {number} interval How often should browser call poll functions (ms)
   * @param {function()} setTimeout Reference to a real or fake `setTimeout` function.
   *
   * @description
   * Configures the poller to run in the specified intervals, using the specified
   * setTimeout fn and kicks it off.
   */
  function startPoller(interval, setTimeout) {
    (function check() {
      forEach(pollFns, function(pollFn){ pollFn(); });
      pollTimeout = setTimeout(check, interval);
    })();
  }

  //////////////////////////////////////////////////////////////
  // URL API
  //////////////////////////////////////////////////////////////

  var lastBrowserUrl = location.href,
      baseElement = document.find('base'),
      newLocation = null;

  /**
   * @name ng.$browser#url
   * @methodOf ng.$browser
   *
   * @description
   * GETTER:
   * Without any argument, this method just returns current value of location.href.
   *
   * SETTER:
   * With at least one argument, this method sets url to new value.
   * If html5 history api supported, pushState/replaceState is used, otherwise
   * location.href/location.replace is used.
   * Returns its own instance to allow chaining
   *
   * NOTE: this api is intended for use only by the $location service. Please use the
   * {@link ng.$location $location service} to change url.
   *
   * @param {string} url New url (when used as setter)
   * @param {boolean=} replace Should new url replace current history record ?
   */
  self.url = function(url, replace) {
    // Android Browser BFCache causes location, history reference to become stale.
    if (location !== window.location) location = window.location;
    if (history !== window.history) history = window.history;

    // setter
    if (url) {
      if (lastBrowserUrl == url) return;
      lastBrowserUrl = url;
      if ($sniffer.history) {
        if (replace) history.replaceState(null, '', url);
        else {
          history.pushState(null, '', url);
          // Crazy Opera Bug: http://my.opera.com/community/forums/topic.dml?id=1185462
          baseElement.attr('href', baseElement.attr('href'));
        }
      } else {
        newLocation = url;
        if (replace) {
          location.replace(url);
        } else {
          location.href = url;
        }
      }
      return self;
    // getter
    } else {
      // - newLocation is a workaround for an IE7-9 issue with location.replace and location.href
      //   methods not updating location.href synchronously.
      // - the replacement is a workaround for https://bugzilla.mozilla.org/show_bug.cgi?id=407172
      return newLocation || location.href.replace(/%27/g,"'");
    }
  };

  var urlChangeListeners = [],
      urlChangeInit = false;

  function fireUrlChange() {
    newLocation = null;
    if (lastBrowserUrl == self.url()) return;

    lastBrowserUrl = self.url();
    forEach(urlChangeListeners, function(listener) {
      listener(self.url());
    });
  }

  /**
   * @name ng.$browser#onUrlChange
   * @methodOf ng.$browser
   * @TODO(vojta): refactor to use node's syntax for events
   *
   * @description
   * Register callback function that will be called, when url changes.
   *
   * It's only called when the url is changed from outside of angular:
   * - user types different url into address bar
   * - user clicks on history (forward/back) button
   * - user clicks on a link
   *
   * It's not called when url is changed by $browser.url() method
   *
   * The listener gets called with new url as parameter.
   *
   * NOTE: this api is intended for use only by the $location service. Please use the
   * {@link ng.$location $location service} to monitor url changes in angular apps.
   *
   * @param {function(string)} listener Listener function to be called when url changes.
   * @return {function(string)} Returns the registered listener fn - handy if the fn is anonymous.
   */
  self.onUrlChange = function(callback) {
    if (!urlChangeInit) {
      // We listen on both (hashchange/popstate) when available, as some browsers (e.g. Opera)
      // don't fire popstate when user change the address bar and don't fire hashchange when url
      // changed by push/replaceState

      // html5 history api - popstate event
      if ($sniffer.history) jqLite(window).on('popstate', fireUrlChange);
      // hashchange event
      if ($sniffer.hashchange) jqLite(window).on('hashchange', fireUrlChange);
      // polling
      else self.addPollFn(fireUrlChange);

      urlChangeInit = true;
    }

    urlChangeListeners.push(callback);
    return callback;
  };

  //////////////////////////////////////////////////////////////
  // Misc API
  //////////////////////////////////////////////////////////////

  /**
   * @name ng.$browser#baseHref
   * @methodOf ng.$browser
   *
   * @description
   * Returns current <base href>
   * (always relative - without domain)
   *
   * @returns {string=} current <base href>
   */
  self.baseHref = function() {
    var href = baseElement.attr('href');
    return href ? href.replace(/^(https?\:)?\/\/[^\/]*/, '') : '';
  };

  //////////////////////////////////////////////////////////////
  // Cookies API
  //////////////////////////////////////////////////////////////
  var lastCookies = {};
  var lastCookieString = '';
  var cookiePath = self.baseHref();

  /**
   * @name ng.$browser#cookies
   * @methodOf ng.$browser
   *
   * @param {string=} name Cookie name
   * @param {string=} value Cookie value
   *
   * @description
   * The cookies method provides a 'private' low level access to browser cookies.
   * It is not meant to be used directly, use the $cookie service instead.
   *
   * The return values vary depending on the arguments that the method was called with as follows:
   *
   * - cookies() -> hash of all cookies, this is NOT a copy of the internal state, so do not modify
   *   it
   * - cookies(name, value) -> set name to value, if value is undefined delete the cookie
   * - cookies(name) -> the same as (name, undefined) == DELETES (no one calls it right now that
   *   way)
   *
   * @returns {Object} Hash of all cookies (if called without any parameter)
   */
  self.cookies = function(name, value) {
    /* global escape: false, unescape: false */
    var cookieLength, cookieArray, cookie, i, index;

    if (name) {
      if (value === undefined) {
        rawDocument.cookie = escape(name) + "=;path=" + cookiePath +
                                ";expires=Thu, 01 Jan 1970 00:00:00 GMT";
      } else {
        if (isString(value)) {
          cookieLength = (rawDocument.cookie = escape(name) + '=' + escape(value) +
                                ';path=' + cookiePath).length + 1;

          // per http://www.ietf.org/rfc/rfc2109.txt browser must allow at minimum:
          // - 300 cookies
          // - 20 cookies per unique domain
          // - 4096 bytes per cookie
          if (cookieLength > 4096) {
            $log.warn("Cookie '"+ name +
              "' possibly not set or overflowed because it was too large ("+
              cookieLength + " > 4096 bytes)!");
          }
        }
      }
    } else {
      if (rawDocument.cookie !== lastCookieString) {
        lastCookieString = rawDocument.cookie;
        cookieArray = lastCookieString.split("; ");
        lastCookies = {};

        for (i = 0; i < cookieArray.length; i++) {
          cookie = cookieArray[i];
          index = cookie.indexOf('=');
          if (index > 0) { //ignore nameless cookies
            name = unescape(cookie.substring(0, index));
            // the first value that is seen for a cookie is the most
            // specific one.  values for the same cookie name that
            // follow are for less specific paths.
            if (lastCookies[name] === undefined) {
              lastCookies[name] = unescape(cookie.substring(index + 1));
            }
          }
        }
      }
      return lastCookies;
    }
  };


  /**
   * @name ng.$browser#defer
   * @methodOf ng.$browser
   * @param {function()} fn A function, who's execution should be deferred.
   * @param {number=} [delay=0] of milliseconds to defer the function execution.
   * @returns {*} DeferId that can be used to cancel the task via `$browser.defer.cancel()`.
   *
   * @description
   * Executes a fn asynchronously via `setTimeout(fn, delay)`.
   *
   * Unlike when calling `setTimeout` directly, in test this function is mocked and instead of using
   * `setTimeout` in tests, the fns are queued in an array, which can be programmatically flushed
   * via `$browser.defer.flush()`.
   *
   */
  self.defer = function(fn, delay) {
    var timeoutId;
    outstandingRequestCount++;
    timeoutId = setTimeout(function() {
      delete pendingDeferIds[timeoutId];
      completeOutstandingRequest(fn);
    }, delay || 0);
    pendingDeferIds[timeoutId] = true;
    return timeoutId;
  };


  /**
   * @name ng.$browser#defer.cancel
   * @methodOf ng.$browser.defer
   *
   * @description
   * Cancels a deferred task identified with `deferId`.
   *
   * @param {*} deferId Token returned by the `$browser.defer` function.
   * @returns {boolean} Returns `true` if the task hasn't executed yet and was successfully
   *                    canceled.
   */
  self.defer.cancel = function(deferId) {
    if (pendingDeferIds[deferId]) {
      delete pendingDeferIds[deferId];
      clearTimeout(deferId);
      completeOutstandingRequest(noop);
      return true;
    }
    return false;
  };

}
@param {object} window The global window object.
@param {object} document jQuery wrapped document.
@param {function()} XHR XMLHttpRequest constructor.
@param {object} $log console.log or an object with the same interface.
@param {object} $sniffer $sniffer service