Reland a11y keyboard.

BUG=297132

Patch set 1 is the original CL:

https://codereview.chromium.org/137543002/

which broke tests on the memory bots. Path set 2 contains the fix for the test failure.

Review URL: https://codereview.chromium.org/148213010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247784 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247784