Add development Blink setting for impl-side rubber-banding

Source/platform/mac/ScrollAnimatorMac.mm

 /*
  * Copyright (C) 2010, 2011 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.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 1062 matching lines @@
         didEndScrollGesture();
     else if (phase == PlatformWheelEventPhaseMayBegin)
         mayBeginScrollGesture();
 }
 
 #if USE(RUBBER_BANDING)
 bool ScrollAnimatorMac::handleWheelEvent(const PlatformWheelEvent& wheelEvent)
 {
     m_haveScrolledSincePageLoad = true;
 
-    if (!wheelEvent.hasPreciseScrollingDeltas() || !rubberBandingEnabledForSystem())
+    if (!wheelEvent.hasPreciseScrollingDeltas() || !rubberBandingEnabledForSystem() || m_scrollableArea->rubberBandingOnCompositorThread())
         return ScrollAnimator::handleWheelEvent(wheelEvent);
 
     // FIXME: This is somewhat roundabout hack to allow forwarding wheel events
     // up to the parent scrollable area. It takes advantage of the fact that
     // the base class implementation of handleWheelEvent will not accept the
     // wheel event if there is nowhere to scroll.
     if (fabsf(wheelEvent.deltaY()) >= fabsf(wheelEvent.deltaX())) {
         if (!allowsVerticalStretching())
             return ScrollAnimator::handleWheelEvent(wheelEvent);
     } else {
@@ skipping 266 matching lines @@
         return;
 
     m_visibleScrollerThumbRect = rectInViewCoordinates;
 }
 
 bool ScrollAnimatorMac::canUseCoordinatedScrollbar() {
     return ScrollbarThemeMacCommon::isOverlayAPIAvailable();
 }
 
 } // namespace blink