Making GraphicsContext the owner of PlatformContext.

Source/core/page/FrameView.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 2972 matching lines @@
 
     RenderView* renderView = this->renderView();
     if ((renderView && renderView->theme()->supportsControlTints()) || hasCustomScrollbars())
         paintControlTints();
 }
 
 void FrameView::paintControlTints()
 {
     if (needsLayout())
         layout();
-    PlatformGraphicsContext* const noContext = 0;
-    GraphicsContext context(noContext);
+    GraphicsContext context(0); // NULL canvas to get a non-painting context.

[jamesr, 2013/04/29 23:56:17]

woah, so this does a "paint" just to update random bits of state? weird!

     context.setUpdatingControlTints(true);
     paint(&context, frameRect());
 }
 
 bool FrameView::wasScrolledByUser() const
 {
     return m_wasScrolledByUser;
 }
 
 void FrameView::setWasScrolledByUser(bool wasScrolledByUser)
@@ skipping 526 matching lines @@
 }
 
 AXObjectCache* FrameView::axObjectCache() const
 {
     if (frame() && frame()->document())
         return frame()->document()->existingAXObjectCache();
     return 0;
 }
     
 } // namespace WebCore