Media Galleries API Metadata: Enable GetMetadata call and fix bugs

BUG=31840,332228

Review URL: https://codereview.chromium.org/166223003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253116 0039d316-1c4b-4281-b951-d872f2087c98
components: Make components_unittests opt into real GL NullDraw contexts.

This breaks the dependency on the TestCompositor for
this test suite. Once it's no longer in use by any test
suite, we can remove it.

These tests don't compile in the compositor and ui/gl/ on IOS, so don't
initialize GL there.

R=jochen@chromium.org
BUG=270918

Review URL: https://codereview.chromium.org/175583003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253117 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253116
SVN changes up to revision 253117