Revert 256960 because it causes failures in a number of tests.

Test failures in: win8 views unittests (e.g. CloseAnchorViewTest), and
ash unittests (e.g. GlobalAcceleratorsToggleAppList), in chromeos asan
unit-tests (e.g. CreateAndClose), and various other tests.

> Reland (try 2) r256396 Add views implementation for AXTreeSource.
> 
> Original cl:
> http://codereview.chromium.org/173893003
> 
> BUG=318758
> TBR=dtseng@chromium.org
> 
> Review URL: https://codereview.chromium.org/196383008

TBR=dtseng@chromium.org

Review URL: https://codereview.chromium.org/199593005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256973 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 256973