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

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

Index: third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
index 8a3834508490099d27d85458a4d021a0ba34c05c..f9d3059c901bafb3b4770c068a7e70138d7daa35 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
@@ -1464,6 +1464,15 @@ void PaintLayerScrollableArea::resetRebuildScrollbarLayerFlags()
     m_rebuildVerticalScrollbarLayer = false;
 }
 
+CompositorAnimationTimeline* PaintLayerScrollableArea::compositorAnimationTimeline() const
+{
+    if (LocalFrame* frame = box().frame()) {
+        if (Page* page = frame->page())
+            return page->scrollingCoordinator() ? page->scrollingCoordinator()->compositorAnimationTimeline() : 0;

[jbroman, 2016/03/14 17:35:32]

Prefer nullptr to 0.

[ymalik, 2016/03/14 21:45:39]

Done.

+    }
+    return nullptr;
+}
+
 PaintLayerScrollableArea::ScrollbarManager::ScrollbarManager(PaintLayerScrollableArea& scrollableArea)
     : m_scrollableArea(&scrollableArea)
     , m_canDetachScrollbars(0)