Code:   const net::HttpRequestHeaders& request_headers() const {
    return request_headers_;
  }

Commit Message: Fix ChromeResourceDispatcherHostDelegateMirrorBrowserTest.MirrorRequestHeader with network service.

The functionality worked, as part of converting DICE, however the test code didn't work since it
depended on accessing the net objects directly. Switch the tests to use the EmbeddedTestServer, to
better match production, which removes the dependency on net/.

Also:
-make GetFilePathWithReplacements replace strings in the mock headers if they're present
-add a global to google_util to ignore ports; that way other tests can be converted without having
  to modify each callsite to google_util

Bug: 881976
Change-Id: Ic52023495c1c98c1248025c11cdf37f433fef058
Reviewed-on: https://chromium-review.googlesource.com/c/1328142
Commit-Queue: John Abd-El-Malek <jam@chromium.org>
Reviewed-by: Ramin Halavati <rhalavati@chromium.org>
Reviewed-by: Maks Orlovich <morlovich@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607652}
CWE ID: 
  const net::HttpRequestHeaders& request_headers() const {
