Fixed mismatched channel order in OSMesaViewGLContext.

Made failing SwapBuffers not an error. We have a race condition whereby a window can be closed while the GPU process is rendering. This could make ui and browser tests flaky.

TEST=try, make sure color channels are not reversed
BUG=none

Review URL: http://codereview.chromium.org/4281003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@64858 0039d316-1c4b-4281-b951-d872f2087c98