Support dynamic switching between integrated and discrete GPUs on Mac OS X.

ui/gfx/gl/gl_share_group.h

Index: ui/gfx/gl/gl_share_group.h
===================================================================
--- ui/gfx/gl/gl_share_group.h	(revision 104937)
+++ ui/gfx/gl/gl_share_group.h	(working copy)
@@ -30,6 +30,10 @@
   // there are no initialized contexts in the share group.
   void* GetHandle();
 
+  // Returns a pointer to any initialized context in the share group
+  // or NULL if there are no initialized contexts in the share group.
+  GLContext* GetContext();
+
  private:
   friend class base::RefCounted<GLShareGroup>;
   ~GLShareGroup();