Scroll offset animation curve retargeting.

cc/animation/scroll_offset_animation_curve.h

Index: cc/animation/scroll_offset_animation_curve.h
diff --git a/cc/animation/scroll_offset_animation_curve.h b/cc/animation/scroll_offset_animation_curve.h
index 543ae373f94edd6d3563b27c416de90c2044e07c..3d71e13c729ba44beb869e34bba51af4574907f5 100644
--- a/cc/animation/scroll_offset_animation_curve.h
+++ b/cc/animation/scroll_offset_animation_curve.h
@@ -24,6 +24,8 @@ class CC_EXPORT ScrollOffsetAnimationCurve : public AnimationCurve {
 
   void SetInitialValue(const gfx::Vector2dF& initial_value);
   gfx::Vector2dF GetValue(double t) const;
+  gfx::Vector2dF target_value() const { return target_value_; }
+  void UpdateTarget(double t, const gfx::Vector2dF& new_target);
 
   // AnimationCurve implementation
   virtual double Duration() const OVERRIDE;
@@ -36,7 +38,10 @@ class CC_EXPORT ScrollOffsetAnimationCurve : public AnimationCurve {
 
   gfx::Vector2dF initial_value_;
   gfx::Vector2dF target_value_;
-  base::TimeDelta duration_;
+  base::TimeDelta total_animation_duration_;
+
+  // Time from animation start to most recent UpdateTarget.
+  base::TimeDelta last_retarget_;
 
   scoped_ptr<TimingFunction> timing_function_;