GPU: Keep track of the last real context and real surface made current.

ui/gl/gl_context_nsview.h

Index: ui/gl/gl_context_nsview.h
diff --git a/ui/gl/gl_context_nsview.h b/ui/gl/gl_context_nsview.h
index bb2aa78107ba595553f79f7d7ee32c00a89ce72f..f4f4df713baf0c44f81159b86156e24e35497155 100644
--- a/ui/gl/gl_context_nsview.h
+++ b/ui/gl/gl_context_nsview.h
@@ -17,7 +17,7 @@ class GLSurface;
 
 // GLContextNSView encapsulates an NSView-based GLContext.  This is paired with
 // the GLSurfaceNSView class.
-class GLContextNSView : public GLContext {
+class GLContextNSView : public GLContextReal {
  public:
   explicit GLContextNSView(GLShareGroup* group);
   virtual ~GLContextNSView();