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 694bf45f272a36c628b21b201db7edd86683b36d..b4db88b366b11645d017426febdfeef28b88c55b 100644
--- a/cc/trees/draw_property_utils.cc
+++ b/cc/trees/draw_property_utils.cc
@@ -373,7 +373,7 @@ void CalculateVisibleRects(
 
     int effect_ancestor_with_copy_request =
         effect_tree.ClosestAncestorWithCopyRequest(layer->effect_tree_index());
-    if (effect_ancestor_with_copy_request > 1) {
+    if (effect_ancestor_with_copy_request > EffectTree::kRootNodeId) {
       // Non root copy request.
       ConditionalClip accumulated_clip_rect = ComputeAccumulatedClip(
           clip_tree, layer->clip_tree_index(), effect_tree,
@@ -721,10 +721,11 @@ 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->clip);
       clip_node->clip_in_target_space = clip_node->clip;
       clip_node->combined_clip_in_target_space = clip_node->clip;
@@ -877,20 +878,22 @@ 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->target_id = 0;
+      node->target_id = EffectTree::kRootNodeId;
     } else if (!can_render_to_separate_surface) {
-      node->target_id = 1;
+      node->target_id = EffectTree::kRootNodeId;
     } else if (effect_tree->parent(node)->has_render_surface) {
       node->target_id = node->parent_id;
     } else {
@@ -902,7 +905,8 @@ 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);
 }
@@ -911,7 +915,7 @@ 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->render_surface;
   gfx::Rect root_clip =
@@ -953,7 +957,7 @@ 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);
   }
 
   ConditionalClip accumulated_clip_rect =
@@ -1182,7 +1186,7 @@ static void SetSurfaceDrawTransform(const TransformTree& transform_tree,
   const EffectNode* effect_node =
       effect_tree.Node(render_surface->EffectTreeIndex());
   // The draw transform of root render surface is identity tranform.
-  if (transform_node->id == 1) {
+  if (transform_node->id == TransformTree::kRootNodeId) {
     render_surface->SetDrawTransform(gfx::Transform());
     return;
   }