Implement TTS dispatcher using RenderProcessObserver instead of MessageFilter.

That guarantees the logic happens on the right thread.

BUG=171887
NOTRY=true

Review URL: https://chromiumcodereview.appspot.com/15031002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@198786 0039d316-1c4b-4281-b951-d872f2087c98
2 files changed