function _runnerEndHandler(event, reporter) {
        if (resultsPath && resultsPath.substr(-5) === ".json") {
            writeResults(resultsPath, reporter.toJSON());
        }

        _writeResults.always(function () { brackets.app.quit(); });
    }
Listener for UnitTestReporter "runnerEnd" event. Attached only if
"resultsPath" URL parameter exists. Does not overwrite existing file.

@param {!$.Event} event
@param {!UnitTestReporter} reporter