cc: Move SyncedScrollOffset to scroll tree

cc/layers/layer.cc

Index: cc/layers/layer.cc
diff --git a/cc/layers/layer.cc b/cc/layers/layer.cc
index 1441ccd64887db87b2b26c8e66c9bcd6e3d6d0d5..fc4629ce9d1a0a78f045d93abc9bd30e934f41f3 100644
--- a/cc/layers/layer.cc
+++ b/cc/layers/layer.cc
@@ -884,6 +884,11 @@ void Layer::SetScrollOffset(const gfx::ScrollOffset& scroll_offset) {
   if (!layer_tree_host_)
     return;
 
+  if (scroll_tree_index() != -1 && scrollable())
+    layer_tree_host_->property_trees()
+        ->scroll_tree.synced_scroll_offset(id())
+        ->PushFromMainThread(scroll_offset);

[ajuma, 2016/03/01 22:54:20]

How about adding a SetScrollOffset method to ScrollTree, that takes an id and
scroll offset?

[sunxd, 2016/03/02 17:45:34]

Done.

+
   if (TransformNode* transform_node =
           layer_tree_host_->property_trees()->transform_tree.Node(
               transform_tree_index())) {
@@ -923,6 +928,12 @@ void Layer::SetScrollOffsetFromImplSide(
   SetNeedsPushProperties();
 
   bool needs_rebuild = true;
+
+  if (scroll_tree_index() != -1 && scrollable())
+    layer_tree_host_->property_trees()
+        ->scroll_tree.synced_scroll_offset(id())
+        ->PushFromMainThread(scroll_offset);
+
   if (TransformNode* transform_node =
           layer_tree_host_->property_trees()->transform_tree.Node(
               transform_tree_index())) {
@@ -1339,9 +1350,10 @@ void Layer::PushPropertiesTo(LayerImpl* layer) {
   // active tree. To do so, avoid scrolling the pending tree along with it
   // instead of trying to undo that scrolling later.
   if (ScrollOffsetAnimationWasInterrupted())
-    layer->PushScrollOffsetFromMainThreadAndClobberActiveValue(scroll_offset_);
-  else
-    layer->PushScrollOffsetFromMainThread(scroll_offset_);
+    layer_tree_host()
+        ->property_trees()
+        ->scroll_tree.synced_scroll_offset(layer->id())
+        ->set_clobber_active_value();
   layer->SetScrollCompensationAdjustment(ScrollCompensationAdjustment());
 
   {