cc: Stop creating unused 0 property tree nodes other than transform

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 <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 1223 matching lines @@
   EffectNode* node = effect_tree.Node(effect_tree_index_);
   return node->data.screen_space_opacity == 0.f;
 }
 
 bool LayerImpl::InsideReplica() const {
   // There are very few render targets so this should be cheap to do for each
   // layer instead of something more complicated.
   EffectTree& effect_tree = layer_tree_impl_->property_trees()->effect_tree;
   EffectNode* node = effect_tree.Node(effect_tree_index_);
 
-  while (node->id > 0) {
-    if (node->data.replica_layer_id != -1)
+  while (node->id > EffectTree::kRootNodeId) {
+    if (node->data.replica_layer_id != EffectTree::kInvalidNodeId)

[ajuma, 2016/06/22 13:29:50]

Layer::INVALID_ID since this is a layer id

       return true;
     node = effect_tree.Node(node->data.target_id);
   }
 
-  return false;
+  return node->data.replica_layer_id != EffectTree::kInvalidNodeId;

[ajuma, 2016/06/22 13:29:50]

Here too, Layer::INVALID_ID

 }
 
 float LayerImpl::GetIdealContentsScale() const {
   float page_scale = IsAffectedByPageScale()
                          ? layer_tree_impl()->current_page_scale_factor()
                          : 1.f;
   float device_scale = layer_tree_impl()->device_scale_factor();
 
   float default_scale = page_scale * device_scale;
   if (!layer_tree_impl()
            ->settings()
            .layer_transforms_should_scale_layer_contents) {
     return default_scale;
   }
 
   gfx::Vector2dF transform_scales = MathUtil::ComputeTransform2dScaleComponents(
       ScreenSpaceTransform(), default_scale);
   return std::max(transform_scales.x(), transform_scales.y());
 }
 
 }  // namespace cc