Use stub GL draw/clear calls for browser tests that do not need pixels.

Instead of using the "TestCompositor" use real GL contexts that just
stub out these expensive functions.

Previously browser tests that did not disable the test compositor
would fall into legacy software mode in the renderer, causing the
renderer to produce frames in a way we don't ship. Now all tests
will use a compositor in both the browser and the renderers.

This allows us to remove the concept the "test compositor" from
browser tests (and from unit tests if we want).

R=piman@chromium.org, sky
BUG=270918

Review URL: https://codereview.chromium.org/120313002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246107 0039d316-1c4b-4281-b951-d872f2087c98
Ignore multiple NOTIFICATION_EXTENSION_VIEW_REGISTERED messages rather than CHECKing them.

BUG=294687

Review URL: https://codereview.chromium.org/139783008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246108 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246108