Implement pinch-zoom scaling for main-frame scrollbars and pinch-zoom overlay scrollbars.

cc/animation_events.h

Index: cc/animation_events.h
diff --git a/cc/animation_events.h b/cc/animation_events.h
index 69b44bca2652cc43d3b16cd35d94c5e793f3d13e..a7fa8cfa032dd7e188c14baec4991251c921ec8c 100644
--- a/cc/animation_events.h
+++ b/cc/animation_events.h
@@ -12,14 +12,15 @@
 namespace cc {
 
 struct AnimationEvent {
-    enum Type { Started, Finished };
+    enum Type { Started, Finished, PropertyUpdate };
 
-    AnimationEvent(Type type, int layerId, int groupId, Animation::TargetProperty targetProperty, double monotonicTime)
+    AnimationEvent(Type type, int layerId, int groupId, Animation::TargetProperty targetProperty, double monotonicTime, float val = 0)
         : type(type)
         , layerId(layerId)
         , groupId(groupId)
         , targetProperty(targetProperty)
         , monotonicTime(monotonicTime)
+        , value(val)
     {
     }
 
@@ -28,6 +29,7 @@ struct AnimationEvent {
     int groupId;
     Animation::TargetProperty targetProperty;
     double monotonicTime;
+    float value;
 };
 
 typedef std::vector<AnimationEvent> AnimationEventsVector;