Add Blink-side flag for enabling/disabling layer squashing.

Source/core/testing/InternalSettings.h

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  * Copyright (C) 2013 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 49 matching lines @@
         float m_originalAccessibilityFontScaleFactor;
         String m_originalMediaTypeOverride;
         bool m_originalMockScrollbarsEnabled;
         bool m_langAttributeAwareFormControlUIEnabled;
         bool m_imagesEnabled;
         bool m_shouldDisplaySubtitles;
         bool m_shouldDisplayCaptions;
         bool m_shouldDisplayTextDescriptions;
         String m_defaultVideoPosterURL;
         bool m_originalCompositorDrivenAcceleratedScrollEnabled;
+        bool m_originalLayerSquashingEnabled;
         bool m_originalPasswordGenerationDecorationEnabled;
     };
 
     static PassRefPtr<InternalSettings> create(Page* page)
     {
         return adoptRef(new InternalSettings(page));
     }
     static InternalSettings* from(Page*);
     void hostDestroyed() { m_page = 0; }
 
@@ skipping 17 matching lines @@
     void setTextAutosizingEnabled(bool, ExceptionState&);
     void setAccessibilityFontScaleFactor(float fontScaleFactor, ExceptionState&);
     void setTextAutosizingWindowSizeOverride(int width, int height, ExceptionState&);
     void setTouchEventEmulationEnabled(bool, ExceptionState&);
     void setViewportEnabled(bool, ExceptionState&);
 
     // FIXME: This is a temporary flag and should be removed once accelerated
     // overflow scroll is ready (crbug.com/254111).
     void setCompositorDrivenAcceleratedScrollingEnabled(bool, ExceptionState&);
 
+    // FIXME: This is a temporary flag and should be removed once squashing is
+    // ready (crbug.com/261605).
+    void setLayerSquashingEnabled(bool, ExceptionState&);
+
     // FIXME: The following are RuntimeEnabledFeatures and likely
     // cannot be changed after process start. These setters should
     // be removed or moved onto internals.runtimeFlags:
     void setAuthorShadowDOMForAnyElementEnabled(bool);
     void setCSSExclusionsEnabled(bool);
     void setExperimentalWebSocketEnabled(bool);
     void setLangAttributeAwareFormControlUIEnabled(bool);
     void setOverlayScrollbarsEnabled(bool);
     void setStyleScopedEnabled(bool);
 
 private:
     explicit InternalSettings(Page*);
 
     Settings* settings() const;
     Page* page() const { return m_page; }
     static const char* supplementName();
 
     Page* m_page;
     Backup m_backup;
 };
 
 } // namespace WebCore
 
 #endif