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

Source/core/testing/InternalSettings.idl

 /*
  * Copyright (C) 2012 Google 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.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 32 matching lines @@
     [RaisesException] void setEditingBehavior(DOMString behavior);
     [RaisesException] void setPasswordGenerationDecorationEnabled(boolean enabled);
     [RaisesException] void setImagesEnabled(boolean enabled);
     [RaisesException] void setDefaultVideoPosterURL(DOMString poster);
     [RaisesException] void setViewportEnabled(boolean enabled);
 
     // FIXME: This is a temporary flag and should be removed once accelerated
     // overflow scroll is ready (crbug.com/254111).
     [RaisesException] void setCompositorDrivenAcceleratedScrollingEnabled(boolean enabled);
 
+    // FIXME: This is a temporary flag and should be removed once squashing is
+    // ready (crbug.com/261605).
+    [RaisesException] void setLayerSquashingEnabled(boolean enabled);
+
     // 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(boolean enabled);
     void setCSSExclusionsEnabled(boolean enabled);
     void setExperimentalWebSocketEnabled(boolean enabled);
     void setLangAttributeAwareFormControlUIEnabled(boolean enabled);
     void setOverlayScrollbarsEnabled(boolean enabled);
     void setStyleScopedEnabled(boolean enabled);
 };