Fix retargeting of composited smooth scrolls from the main thread.

third_party/WebKit/Source/platform/scroll/ScrollAnimator.h

Index: third_party/WebKit/Source/platform/scroll/ScrollAnimator.h
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollAnimator.h b/third_party/WebKit/Source/platform/scroll/ScrollAnimator.h
index 5d8f20a3f84d00c41494120eae3ec0b660651b00..8bc8caa05225a50162a4d859b4d5a876ab02c5f4 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollAnimator.h
+++ b/third_party/WebKit/Source/platform/scroll/ScrollAnimator.h
@@ -65,13 +65,17 @@ public:
 
 protected:
     OwnPtr<WebScrollOffsetAnimationCurve> m_animationCurve;
-    double m_lastTickTime;
     double m_startTime;
     WTF::TimeFunction m_timeFunction;
 
 private:
     FloatPoint desiredTargetPosition() const;
 
+    // Returns true if the animation was scheduled successfully. If animation
+    // could not be scheduled (e.g. because the frame is detached), scrolls
+    // immediately to the target and returns false.
+    bool registerAndScheduleAnimation();
+
     FloatPoint m_targetOffset;
 };