[devtools] Add a command to emulate the default background color.

third_party/WebKit/Source/core/frame/FrameView.h

 /*
    Copyright (C) 1997 Martin Jones (mjones@kde.org)
              (C) 1998 Waldo Bastian (bastian@kde.org)
              (C) 1998, 1999 Torben Weis (weis@kde.org)
              (C) 1999 Lars Knoll (knoll@kde.org)
              (C) 1999 Antti Koivisto (koivisto@kde.org)
    Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights
    reserved.
 
    This library is free software; you can redistribute it and/or
@@ skipping 1009 matching lines @@
   void updateRenderThrottlingStatus(bool hidden, bool subtreeThrottled);
   void notifyResizeObservers();
 
   // PaintInvalidationCapableScrollableArea
   LayoutScrollbarPart* resizer() const override { return nullptr; }
 
   bool checkLayoutInvalidationIsAllowed() const;
 
   PaintController* paintController() { return m_paintController.get(); }
 
+  void updateOpaquenessIfNeeded();
+
   LayoutSize m_size;
 
   typedef HashSet<RefPtr<LayoutEmbeddedObject>> EmbeddedObjectSet;
   EmbeddedObjectSet m_partUpdateSet;
 
   // FIXME: These are just "children" of the FrameView and should be
   // Member<Widget> instead.
   HashSet<RefPtr<LayoutPart>> m_parts;
 
   // The RefPtr cycle between LocalFrame and FrameView is broken
@@ skipping 133 matching lines @@
       HeapLinkedHashSet<WeakMember<ScrollableArea>>;
   AnchoringAdjustmentQueue m_anchoringAdjustmentQueue;
 
   // ScrollbarManager holds the Scrollbar instances.
   ScrollbarManager m_scrollbarManager;
 
   bool m_needsScrollbarsUpdate;
   bool m_suppressAdjustViewSize;
   bool m_allowsLayoutInvalidationAfterLayoutClean;
 
+  bool m_needsOpaquenessUpdate;
+
   Member<ElementVisibilityObserver> m_visibilityObserver;
 
   IntRect m_remoteViewportIntersection;
 
   // For testing.
   struct ObjectPaintInvalidation {
     String name;
     PaintInvalidationReason reason;
   };
   std::unique_ptr<Vector<ObjectPaintInvalidation>>
@@ skipping 49 matching lines @@
                   widget.isFrameView());
 DEFINE_TYPE_CASTS(FrameView,
                   ScrollableArea,
                   scrollableArea,
                   scrollableArea->isFrameView(),
                   scrollableArea.isFrameView());
 
 }  // namespace blink
 
 #endif  // FrameView_h