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

cc/trees/draw_property_utils.cc

Index: cc/trees/draw_property_utils.cc
diff --git a/cc/trees/draw_property_utils.cc b/cc/trees/draw_property_utils.cc
index 6881a25cc1a3f323a0bbaaf55f6f9a04dcad94a5..e3672b079c1a43176e6cfc08cf6671719fe29d7e 100644
--- a/cc/trees/draw_property_utils.cc
+++ b/cc/trees/draw_property_utils.cc
@@ -508,10 +508,11 @@ void ComputeClips(ClipTree* clip_tree,
                   bool non_root_surfaces_enabled) {
   if (!clip_tree->needs_update())
     return;
-  for (int i = 1; i < static_cast<int>(clip_tree->size()); ++i) {
+  for (int i = ClipTree::kRootNodeId; i < static_cast<int>(clip_tree->size());
+       ++i) {
     ClipNode* clip_node = clip_tree->Node(i);
 
-    if (clip_node->id == 1) {
+    if (clip_node->id == ClipTree::kRootNodeId) {
       ResetIfHasNanCoordinate(&clip_node->data.clip);
       clip_node->data.clip_in_target_space = clip_node->data.clip;
       clip_node->data.combined_clip_in_target_space = clip_node->data.clip;
@@ -648,20 +649,22 @@ void ComputeClips(ClipTree* clip_tree,
 void ComputeTransforms(TransformTree* transform_tree) {
   if (!transform_tree->needs_update())
     return;
-  for (int i = 1; i < static_cast<int>(transform_tree->size()); ++i)
+  for (int i = TransformTree::kRootNodeId;
+       i < static_cast<int>(transform_tree->size()); ++i)
     transform_tree->UpdateTransforms(i);
   transform_tree->set_needs_update(false);
 }
 
 void UpdateRenderTarget(EffectTree* effect_tree,
                         bool can_render_to_separate_surface) {
-  for (int i = 1; i < static_cast<int>(effect_tree->size()); ++i) {
+  for (int i = EffectTree::kRootNodeId;
+       i < static_cast<int>(effect_tree->size()); ++i) {
     EffectNode* node = effect_tree->Node(i);
-    if (i == 1) {
+    if (i == EffectTree::kRootNodeId) {
       // Render target on the first effect node is root.
-      node->data.target_id = 0;
+      node->data.target_id = EffectTree::kRootNodeId;
     } else if (!can_render_to_separate_surface) {

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

This can be combined with the previous condition now that both branches use
kRootNodeId.

-      node->data.target_id = 1;
+      node->data.target_id = EffectTree::kRootNodeId;
     } else if (effect_tree->parent(node)->data.has_render_surface) {
       node->data.target_id = node->parent_id;
     } else {
@@ -673,7 +676,8 @@ void UpdateRenderTarget(EffectTree* effect_tree,
 void ComputeEffects(EffectTree* effect_tree) {
   if (!effect_tree->needs_update())
     return;
-  for (int i = 1; i < static_cast<int>(effect_tree->size()); ++i)
+  for (int i = EffectTree::kRootNodeId;
+       i < static_cast<int>(effect_tree->size()); ++i)
     effect_tree->UpdateEffects(i);
   effect_tree->set_needs_update(false);
 }
@@ -770,7 +774,7 @@ static void ComputeClipsWithEffectTree(PropertyTrees* property_trees) {
   EffectTree* effect_tree = &property_trees->effect_tree;
   const ClipTree* clip_tree = &property_trees->clip_tree;
   const TransformTree* transform_tree = &property_trees->transform_tree;
-  EffectNode* root_effect_node = effect_tree->Node(1);
+  EffectNode* root_effect_node = effect_tree->Node(EffectTree::kRootNodeId);
   const RenderSurfaceImpl* root_render_surface =
       root_effect_node->data.render_surface;
   gfx::Rect root_clip = gfx::ToEnclosingRect(
@@ -812,7 +816,7 @@ static void ComputeLayerClipRect(const PropertyTrees* property_trees,
   // TODO(weiliangc): When effect node has up to date render surface info on
   // compositor thread, no need to check for resourceless draw mode
   if (!property_trees->non_root_surfaces_enabled) {
-    target_node = effect_tree->Node(1);
+    target_node = effect_tree->Node(EffectTree::kRootNodeId);
   }
 
   gfx::RectF accumulated_clip =
@@ -984,7 +988,7 @@ static void SetSurfaceDrawTransform(const TransformTree& tree,
                                     RenderSurfaceImpl* render_surface) {
   const TransformNode* node = tree.Node(render_surface->TransformTreeIndex());
   // The draw transform of root render surface is identity tranform.
-  if (node->id == 1) {
+  if (node->id == TransformTree::kRootNodeId) {
     render_surface->SetDrawTransform(gfx::Transform());
     return;
   }