Ignore should-scroll-on-main-thread if main frame is not scrollable

cc/trees/layer_tree_host_common.h

 // Copyright 2011 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.
 
 #ifndef CC_TREES_LAYER_TREE_HOST_COMMON_H_
 #define CC_TREES_LAYER_TREE_HOST_COMMON_H_
 
 #include <limits>
 #include <vector>
 
@@ skipping 100 matching lines @@
   template <typename LayerType>
   static void CallFunctionForSubtree(
       LayerType* root_layer,
       const base::Callback<void(LayerType* layer)>& function);
 
   // Returns a layer with the given id if one exists in the subtree starting
   // from the given root layer (including mask and replica layers).
   template <typename LayerType>
   static LayerType* FindLayerInSubtree(LayerType* root_layer, int layer_id);
 
+  template <typename LayerType>
+  static LayerType* FindFirstScrollableLayer(LayerType* root_layer);
+
   static Layer* get_child_as_raw_ptr(
       const LayerList& children,
       size_t index) {
     return children[index].get();
   }
 
   static LayerImpl* get_child_as_raw_ptr(
       const OwnedLayerImplList& children,
       size_t index) {
     return children[index];
@@ skipping 46 matching lines @@
 
   for (size_t i = 0; i < root_layer->children().size(); ++i) {
     if (LayerType* found = FindLayerInSubtree(
             get_child_as_raw_ptr(root_layer->children(), i), layer_id))
       return found;
   }
   return NULL;
 }
 
 template <typename LayerType>
+LayerType* LayerTreeHostCommon::FindFirstScrollableLayer(LayerType* layer) {
+  if (!layer)
+    return NULL;
+
+  if (layer->scrollable())
+    return layer;
+
+  for (size_t i = 0; i < layer->children().size(); ++i) {
+    LayerType* current = get_child_as_raw_ptr(layer->children(), i);
+    LayerType* found = FindFirstScrollableLayer(current);
+    if (found)
+      return found;
+  }
+
+  return NULL;
+}
+
+template <typename LayerType>
 void LayerTreeHostCommon::CallFunctionForSubtree(
     LayerType* root_layer,
     const base::Callback<void(LayerType* layer)>& function) {
   function.Run(root_layer);
 
   if (LayerType* mask_layer = root_layer->mask_layer())
     function.Run(mask_layer);
   if (LayerType* replica_layer = root_layer->replica_layer()) {
     function.Run(replica_layer);
     if (LayerType* mask_layer = replica_layer->mask_layer())
@@ skipping 47 matching lines @@
           false,
           false,
           render_surface_layer_list) {
   DCHECK(root_layer);
   DCHECK(render_surface_layer_list);
 }
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_HOST_COMMON_H_