Relanding this with fixes for ash_unittests failures on the windows 8 builder.

Recreate and reinitialize the compositor when we receive the target HWND from the metro viewer process on Windows 8 ASH.

This ensures that the compositor paints on the correct surface.

Fixes a regression which occurred after the latest aura refactoring changes. This resulted in nothing painting
in Windows 8 ASH.

Ben's change to address the metro painting issue was reverted on Dec 20th due to ash_unittest crashes.

This fix works well with the ash_unittests and regular Chrome code path.

TBR'ing beng. Will address comments from him in a followup.

BUG=330179
R=ben@chromium.org, cpu@chromium.org
TBR=ben

Review URL: https://codereview.chromium.org/108893005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242910 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242910