Implement accessible BoundsForRange on Mac.

This allows VoiceOver to interact with individual characters and words
and draw a precise bounding box around the active range.

Depends on: 
1. https://codereview.chromium.org/23983002/ 
2. https://codereview.chromium.org/25943003/ 
3. https://codereview.chromium.org/25987002/

BUG=98977

Review URL: https://codereview.chromium.org/25434005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@235686 0039d316-1c4b-4281-b951-d872f2087c98
Add .isolate for media_perftests.

BUG=310837

Review URL: https://codereview.chromium.org/57873006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@235687 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 235687