Handle direction control in compositor Animations

cc/animation/animation.h

Index: cc/animation/animation.h
diff --git a/cc/animation/animation.h b/cc/animation/animation.h
index f996c38bbb3dd410bad69189955c8533a2b77e00..56f1ff77774cfaaa79a67badec53982476884d9b 100644
--- a/cc/animation/animation.h
+++ b/cc/animation/animation.h
@@ -48,6 +48,8 @@ class CC_EXPORT Animation {
     TargetPropertyEnumSize
   };
 
+  enum Direction { Normal, Reverse, Alternate, AlternateReverse };
+
   static scoped_ptr<Animation> Create(scoped_ptr<AnimationCurve> curve,
                                       int animation_id,
                                       int group_id,
@@ -78,12 +80,8 @@ class CC_EXPORT Animation {
   void Suspend(double monotonic_time);
   void Resume(double monotonic_time);
 
-  // If alternates_direction is true, on odd numbered iterations we reverse the
-  // curve.
-  bool alternates_direction() const { return alternates_direction_; }
-  void set_alternates_direction(bool alternates) {
-    alternates_direction_ = alternates;
-  }
+  Direction direction() { return direction_; }
+  void set_direction(Direction direction) { direction_ = direction; }
 
   bool IsFinishedAt(double monotonic_time) const;
   bool is_finished() const {
@@ -150,7 +148,7 @@ class CC_EXPORT Animation {
   RunState run_state_;
   int iterations_;
   double start_time_;
-  bool alternates_direction_;
+  Direction direction_;
 
   // The time offset effectively pushes the start of the animation back in time.
   // This is used for resuming paused animations -- an animation is added with a