Create PageScaleAnimation after ImplTree is activated.

cc/trees/layer_tree_host.h

Index: cc/trees/layer_tree_host.h
diff --git a/cc/trees/layer_tree_host.h b/cc/trees/layer_tree_host.h
index 7820cc24a29764bb8eb02ffc65cdd352d7a9757b..9b0d777f4adda643e64ff95031911777c7713da1 100644
--- a/cc/trees/layer_tree_host.h
+++ b/cc/trees/layer_tree_host.h
@@ -63,6 +63,7 @@ class ResourceUpdateQueue;
 class SharedBitmapManager;
 class TopControlsManager;
 class UIResourceRequest;
+struct PendingPageScaleAnimation;
 struct RenderingStats;
 struct ScrollAndScaleSet;
 
@@ -433,12 +434,6 @@ class CC_EXPORT LayerTreeHost {
 
   scoped_ptr<AnimationRegistrar> animation_registrar_;
 
-  struct PendingPageScaleAnimation {
-    gfx::Vector2d target_offset;
-    bool use_anchor;
-    float scale;
-    base::TimeDelta duration;
-  };
   scoped_ptr<PendingPageScaleAnimation> pending_page_scale_animation_;
 
   bool in_paint_layer_contents_;