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

cc/trees/property_tree_builder.cc

Index: cc/trees/property_tree_builder.cc
diff --git a/cc/trees/property_tree_builder.cc b/cc/trees/property_tree_builder.cc
index adbffbe9896451235e3951c664dfab072fa857a5..2100b3c55db5ec81da2901163d527edd5e620da7 100644
--- a/cc/trees/property_tree_builder.cc
+++ b/cc/trees/property_tree_builder.cc
@@ -25,10 +25,6 @@ class LayerTreeHost;
 
 namespace {
 
-static const int kInvalidPropertyTreeNodeId = -1;
-static const int kRootPropertyTreeNodeId = 0;
-static const int kViewportClipTreeNodeId = 1;
-
 template <typename LayerType>
 struct DataForRecursion {
   PropertyTrees* property_trees;
@@ -451,7 +447,7 @@ bool AddTransformNodeIfNeeded(
   LayerType* transform_parent = GetTransformParent(data_from_ancestor, layer);
   DCHECK(is_root || transform_parent);
 
-  int parent_index = kRootPropertyTreeNodeId;
+  int parent_index = TransformTree::kDeviceNodeId;
   if (transform_parent)
     parent_index = transform_parent->transform_tree_index();
 
@@ -535,17 +531,22 @@ bool AddTransformNodeIfNeeded(
       ShouldFlattenTransform(layer) || has_surface;
   DCHECK_GT(data_from_ancestor.property_trees->effect_tree.size(), 0u);
 
-  data_for_children->property_trees->transform_tree.SetTargetId(
-      node->id, data_for_children->property_trees->effect_tree
-                    .Node(data_from_ancestor.render_target)
-                    ->data.transform_id);
+  if (data_from_ancestor.render_target == EffectTree::kInvalidNodeId) {
+    data_for_children->property_trees->transform_tree.SetTargetId(
+        node->id, TransformTree::kDeviceNodeId);
+  } else {
+    data_for_children->property_trees->transform_tree.SetTargetId(
+        node->id, data_for_children->property_trees->effect_tree
+                      .Node(data_from_ancestor.render_target)
+                      ->data.transform_id);
+  }
   data_for_children->property_trees->transform_tree.SetContentTargetId(
       node->id, data_for_children->property_trees->effect_tree
                     .Node(data_for_children->render_target)
                     ->data.transform_id);
   DCHECK_NE(
       data_for_children->property_trees->transform_tree.TargetId(node->id),
-      kInvalidPropertyTreeNodeId);
+      TransformTree::kInvalidNodeId);
 
   node->data.has_potential_animation = has_potentially_animated_transform;
   node->data.is_currently_animating = layer->TransformIsAnimating();
@@ -931,8 +932,8 @@ bool AddEffectNodeIfNeeded(
     // into. Transform node created from root layer (includes device scale
     // factor) and clip node created from root layer (include viewports) applies
     // to root render surface's content, but not root render surface itself.
-    node.data.transform_id = kRootPropertyTreeNodeId;
-    node.data.clip_id = kViewportClipTreeNodeId;
+    node.data.transform_id = TransformTree::kDeviceNodeId;
+    node.data.clip_id = ClipTree::kRootNodeId;
   }
   data_for_children->effect_tree_parent = effect_tree.Insert(node, parent_id);
   int node_id = data_for_children->effect_tree_parent;
@@ -995,7 +996,7 @@ void AddScrollNodeIfNeeded(
     if (layer->scroll_clip_layer()) {
       clip_bounds = layer->scroll_clip_layer()->bounds();
       DCHECK(layer->scroll_clip_layer()->transform_tree_index() !=
-             kInvalidPropertyTreeNodeId);
+             TransformTree::kInvalidNodeId);
       node.data.max_scroll_offset_affected_by_page_scale =
           !data_from_ancestor.property_trees->transform_tree
                .Node(layer->scroll_clip_layer()->transform_tree_index())
@@ -1247,10 +1248,10 @@ void BuildPropertyTreesTopLevelInternal(
   data_for_recursion.property_trees = property_trees;
   data_for_recursion.transform_tree_parent = nullptr;
   data_for_recursion.transform_fixed_parent = nullptr;
-  data_for_recursion.render_target = kRootPropertyTreeNodeId;
-  data_for_recursion.clip_tree_parent = kRootPropertyTreeNodeId;
-  data_for_recursion.effect_tree_parent = kInvalidPropertyTreeNodeId;
-  data_for_recursion.scroll_tree_parent = kRootPropertyTreeNodeId;
+  data_for_recursion.render_target = EffectTree::kInvalidNodeId;
+  data_for_recursion.clip_tree_parent = ClipTree::kInvalidNodeId;
+  data_for_recursion.effect_tree_parent = EffectTree::kInvalidNodeId;
+  data_for_recursion.scroll_tree_parent = ScrollTree::kInvalidNodeId;
   data_for_recursion.page_scale_layer = page_scale_layer;
   data_for_recursion.inner_viewport_scroll_layer = inner_viewport_scroll_layer;
   data_for_recursion.outer_viewport_scroll_layer = outer_viewport_scroll_layer;
@@ -1289,10 +1290,10 @@ void BuildPropertyTreesTopLevelInternal(
   root_clip.data.resets_clip = true;
   root_clip.data.applies_local_clip = true;
   root_clip.data.clip = gfx::RectF(viewport);
-  root_clip.data.transform_id = kRootPropertyTreeNodeId;
+  root_clip.data.transform_id = TransformTree::kDeviceNodeId;
   data_for_recursion.clip_tree_parent =
       data_for_recursion.property_trees->clip_tree.Insert(
-          root_clip, kRootPropertyTreeNodeId);
+          root_clip, ClipTree::kInvalidNodeId);
 
   DataForRecursionFromChild<LayerType> data_from_child;
   BuildPropertyTreesInternal(root_layer, data_for_recursion, &data_from_child);