Make sure that each NSWindow has its own GL context

Update the GL context for an NSView before drawing it, in
CreateCompositedIOSurface.

In the case of the devtools window being added and removed,
the WindowFrameChanged is not called on the devtools window,
and as a result, it and the main window compete for the same
context (which sometimes results in nothing being drawn for
the devtools window).

BUG=335011

Review URL: https://codereview.chromium.org/140693013

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246517 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246517