cc: Update transform tree after compositor thread scroll

When LayerImpls scroll, their associated transform trees need to be
updated so that they are correct.

This fixes 17 of the 79 failing tests, when verification is turned on.

R=ajuma@chromium.org,vollick@chromium.org
BUG=481585

Review URL: https://codereview.chromium.org/1141353002

Cr-Commit-Position: refs/heads/master@{#330662}

cc/layers/layer_impl.cc

@@ -1217,15 +1217,29 @@ void LayerImpl::PushScrollOffset(const gfx::ScrollOffset* scroll_offset) {
 }
 
 void LayerImpl::DidUpdateScrollOffset(bool is_from_root_delegate) {
+  DCHECK(scroll_offset_);
+
   if (!is_from_root_delegate)
     layer_tree_impl()->DidUpdateScrollOffset(id());
   NoteLayerPropertyChangedForSubtree();
   ScrollbarParametersDidChange(false);
+
+  // TODO(enne): in the future, scrolling should update the scroll tree
+  // directly instead of going through layers.
+  if (transform_tree_index_ != -1) {
+    TransformTree& transform_tree =
+        layer_tree_impl()->property_trees()->transform_tree;
+    TransformNode* node = transform_tree.Node(transform_tree_index_);
+    node->data.scroll_offset = scroll_offset_->Current(IsActive());
+    node->data.needs_local_transform_update = true;
+    transform_tree.set_needs_update(true);
+  }
+
   // Inform the pending twin that a property changed.
   if (layer_tree_impl()->IsActiveTree()) {
     LayerImpl* pending_twin = layer_tree_impl()->FindPendingTreeLayerById(id());
     if (pending_twin)
-      pending_twin->NoteLayerPropertyChangedForSubtree();
+      pending_twin->DidUpdateScrollOffset(is_from_root_delegate);
   }
 }