First programmatic smooth scroll should run on the compositor if it can

third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@gmail.com>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 1446 matching lines @@
 {
     return box().frame()->view();
 }
 
 void PaintLayerScrollableArea::resetRebuildScrollbarLayerFlags()
 {
     m_rebuildHorizontalScrollbarLayer = false;
     m_rebuildVerticalScrollbarLayer = false;
 }
 
+CompositorAnimationTimeline* PaintLayerScrollableArea::compositorAnimationTimeline() const
+{
+    if (LocalFrame* frame = box().frame()) {
+        if (Page* page = frame->page())
+            return page->scrollingCoordinator() ? page->scrollingCoordinator()->compositorAnimationTimeline() : nullptr;
+    }
+    return nullptr;
+}
+
 PaintLayerScrollableArea::ScrollbarManager::ScrollbarManager(PaintLayerScrollableArea& scrollableArea)
     : m_scrollableArea(&scrollableArea)
     , m_canDetachScrollbars(0)
     , m_hBarIsAttached(0)
     , m_vBarIsAttached(0)
 {
 }
 
 void PaintLayerScrollableArea::ScrollbarManager::dispose()
 {
@@ skipping 97 matching lines @@
 }
 
 DEFINE_TRACE(PaintLayerScrollableArea::ScrollbarManager)
 {
     visitor->trace(m_scrollableArea);
     visitor->trace(m_hBar);
     visitor->trace(m_vBar);
 }
 
 } // namespace blink