Remove a RenderWidgetHostImpl dependency from OverscrollController

The OverscrollController queries the RenderWidgetHostImpl to determine if
an event should be forwarded for dispatch. Eliminate this call by returning
an event disposition, allowing the router to perform the query instead.

BUG=306194

Review URL: https://codereview.chromium.org/27535002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229357 0039d316-1c4b-4281-b951-d872f2087c98
Minor cleanup in P2PSocketHostUdp.

Review URL: https://codereview.chromium.org/27537011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229358 0039d316-1c4b-4281-b951-d872f2087c98
Add renderbuffer BGRA8 format extension and support in cmd buffer for desktop GL. This enables development of a canvas2d msaa flag on desktop systems that use BGRA for canvas2d.

BUG=308277

Review URL: https://codereview.chromium.org/27542003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229359 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 229358
SVN changes up to revision 229359