cc: Ensure pending tree needs prop updates when active tree scrolls.

cc/layers/layer_impl.cc

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/layers/layer_impl.h"
 
 #include "base/json/json_reader.h"
 #include "base/strings/stringprintf.h"
 #include "base/trace_event/trace_event.h"
 #include "base/trace_event/trace_event_argument.h"
@@ skipping 1203 matching lines @@
 
   if (changed)
     DidUpdateScrollOffset(false);
 }
 
 void LayerImpl::DidUpdateScrollOffset(bool is_from_root_delegate) {
   if (!is_from_root_delegate)
     layer_tree_impl()->DidUpdateScrollOffset(id());
   NoteLayerPropertyChangedForSubtree();
   ScrollbarParametersDidChange(false);
+  // 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();
+  }
 }
 
 void LayerImpl::SetDoubleSided(bool double_sided) {
   if (double_sided_ == double_sided)
     return;
 
   double_sided_ = double_sided;
   NoteLayerPropertyChangedForSubtree();
 }
 
@@ skipping 401 matching lines @@
   gfx::Transform scaled_draw_transform =
       draw_properties_.target_space_transform;
   scaled_draw_transform.Scale(SK_MScalar1 / scale, SK_MScalar1 / scale);
   gfx::Size scaled_content_bounds =
       gfx::ToCeiledSize(gfx::ScaleSize(content_bounds(), scale));
   return MathUtil::MapEnclosingClippedRect(scaled_draw_transform,
                                            gfx::Rect(scaled_content_bounds));
 }
 
 }  // namespace cc