Clean up the way layout tests force elements to opt in/out of composited scrolling.

Source/core/testing/Internals.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 196 matching lines @@
     enum {
         // Values need to be kept in sync with Internals.idl.
         LAYER_TREE_INCLUDES_VISIBLE_RECTS = 1,
         LAYER_TREE_INCLUDES_TILE_CACHES = 2,
         LAYER_TREE_INCLUDES_REPAINT_RECTS = 4,
         LAYER_TREE_INCLUDES_PAINTING_PHASES = 8
     };
     String layerTreeAsText(Document*, unsigned flags, ExceptionCode&) const;
     String layerTreeAsText(Document*, ExceptionCode&) const;
 
-    PassRefPtr<NodeList> paintOrderListBeforePromote(Element* element, ExceptionCode& ec);
-    PassRefPtr<NodeList> paintOrderListAfterPromote(Element* element, ExceptionCode& ec);
+    PassRefPtr<NodeList> paintOrderListBeforePromote(Element*, ExceptionCode&);
+    PassRefPtr<NodeList> paintOrderListAfterPromote(Element*, ExceptionCode&);
+
+    enum {
+        // Values need to be kept in sync with Internals.idl.
+        DoNotForceCompositedScrolling = 0,
+        CompositedScrollingAlwaysOn = 1,
+        CompositedScrollingAlwaysOff = 2
+    };
+    void setNeedsCompositedScrolling(Element*, unsigned value, ExceptionCode&);
 
     String repaintRectsAsText(Document*, ExceptionCode&) const;
     String scrollingStateTreeAsText(Document*, ExceptionCode&) const;
     String mainThreadScrollingReasons(Document*, ExceptionCode&) const;
     PassRefPtr<ClientRectList> nonFastScrollableRects(Document*, ExceptionCode&) const;
 
     void garbageCollectDocumentResources(Document*, ExceptionCode&) const;
 
     void allowRoundingHacks() const;
 
@@ skipping 67 matching lines @@
 
     DocumentMarker* markerAt(Node*, const String& markerType, unsigned index, ExceptionCode&);
     RefPtr<DOMWindow> m_frontendWindow;
     OwnPtr<InspectorFrontendChannelDummy> m_frontendChannel;
     RefPtr<InternalRuntimeFlags> m_runtimeFlags;
 };
 
 } // namespace WebCore
 
 #endif