cc : Update render surfaces using LayerListIterator instead of treewalk

cc/trees/layer_tree_impl.cc

 // 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.
 
 #include "cc/trees/layer_tree_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 545 matching lines @@
 void LayerTreeImpl::SetPageScaleOnActiveTree(float active_page_scale) {
   DCHECK(IsActiveTree());
   if (page_scale_factor()->SetCurrent(
           ClampPageScaleFactorToLimits(active_page_scale))) {
     DidUpdatePageScale();
     if (PageScaleLayer()) {
       draw_property_utils::UpdatePageScaleFactor(
           property_trees(), PageScaleLayer(), current_page_scale_factor(),
           device_scale_factor(), layer_tree_host_impl_->DrawTransform());
     } else {
-      DCHECK(!root_layer_ || active_page_scale == 1);
+      DCHECK(!root_layer_ || active_page_scale == 1 ||
+             root_layer_->transform_tree_index() == -1);

[jaydasika, 2016/03/22 00:19:07]

have to remove this (added it to make unit tests pass), but I am unsure about
the alternative. I tried building property trees and setting page scale layer
before this function is called to make the tests take the other path (if
statement), but LayerById(page_scale_layer_id) returns null inspite of that (I
think its because of the ownership of these layers, they are scoped_ptr created
in the test). Any thoughts on what to do ?

[ajuma, 2016/03/22 14:41:55]

Could it be that the page_scale_layer_id is invalid? LayerImpls get added to the
map in their constructor and removed in their destructor, so if the id is valid,
it should be case that LayerById(id) returns non-null. If the
page_scale_layer_id is indeed valid, try adding some logging to
LayerTreeImpl::RegisterLayer and ::UnregisterLayer to see if these are behaving
as expected.

     }
   }
 }
 
 void LayerTreeImpl::PushPageScaleFromMainThread(float page_scale_factor,
                                                 float min_page_scale_factor,
                                                 float max_page_scale_factor) {
   PushPageScaleFactorAndLimits(&page_scale_factor, min_page_scale_factor,
                                max_page_scale_factor);
 }
@@ skipping 1485 matching lines @@
 }
 
 void LayerTreeImpl::ResetAllChangeTracking(PropertyTrees::ResetFlags flag) {
   layers_that_should_push_properties_.clear();
   for (auto* layer : *this)
     layer->ResetChangeTracking();
   property_trees_.ResetAllChangeTracking(flag);
 }
 
 }  // namespace cc