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This makes it possible to provide more helpful spoken feedback when focusing
a toolbar button or infobar button - e.g. it can now read the full text of
the infobar when you move focus to any of its buttons.

BUG=106724
TEST=Adds new unit tests; will need new ChromeVox push to test manually.
Review URL: http://codereview.chromium.org/8850004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@114640 0039d316-1c4b-4281-b951-d872f2087c98