Add browser tests for the Web Speech Recognition API.

Introduce an event-driven timeline utility to verify if everything in
test scenarii is happening on the right thread and in the right order,
and add a simple precheck browser test that opens an HTML test page and
verifies that creating a SpeechRecognition object works.

BUG=301906

Review URL: https://codereview.chromium.org/23500011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228332 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228332