Insantiate ExtensionWebContentsObserver for webviews. This fixes a regression from r229957.

BUG=311433,31633006
R=fsamuel@chromium.org

Review URL: https://codereview.chromium.org/41923006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@231140 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 231140
Add multisample-corruption.html to webgl_conformance_expectations.py

It's timing out on Android gpu bot.

BUG=
TEST=gpu waterfall
R=kbr@chromium.org

Review URL: https://codereview.chromium.org/45413003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@231141 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 231141