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

cc/trees/layer_tree_impl.cc

Index: cc/trees/layer_tree_impl.cc
diff --git a/cc/trees/layer_tree_impl.cc b/cc/trees/layer_tree_impl.cc
index 2c8fbb82b5d1e26fe3cbaf0d547f46bacc1bfebe..399dd6d62e3807f49bdd41761839aed2d5539813 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -160,7 +160,7 @@ void LayerTreeImpl::DidUpdateScrollOffset(int layer_id, int transform_id) {
     return;
   }
 
-  if (transform_id != -1) {
+  if (transform_id != TransformTree::kInvalidNodeId) {
     TransformNode* node = transform_tree.Node(transform_id);
     if (node->scroll_offset != scroll_tree.current_scroll_offset(layer_id)) {
       node->scroll_offset = scroll_tree.current_scroll_offset(layer_id);
@@ -576,7 +576,8 @@ void LayerTreeImpl::SetCurrentlyScrollingLayer(LayerImpl* layer) {
   ScrollNode* scroll_node = scroll_tree.CurrentlyScrollingNode();
   int old_id = scroll_node ? scroll_node->owner_id : Layer::INVALID_ID;
   int new_id = layer ? layer->id() : Layer::INVALID_ID;
-  int new_scroll_node_id = layer ? layer->scroll_tree_index() : -1;
+  int new_scroll_node_id =
+      layer ? layer->scroll_tree_index() : ScrollTree::kInvalidNodeId;
   if (layer)
     last_scrolled_layer_id_ = new_id;
 
@@ -1661,7 +1662,7 @@ static bool PointIsClippedByAncestorClipNode(
   // ancestor render surface.
 
   // We first check if the point is clipped by viewport.
-  const ClipNode* clip_node = clip_tree.Node(1);
+  const ClipNode* clip_node = clip_tree.Node(ClipTree::kViewportNodeId);
   gfx::Rect combined_clip_in_target_space =
       gfx::ToEnclosingRect(clip_node->combined_clip_in_target_space);
   if (!PointHitsRect(screen_space_point, gfx::Transform(),
@@ -1669,7 +1670,8 @@ static bool PointIsClippedByAncestorClipNode(
     return true;
 
   for (const ClipNode* clip_node = clip_tree.Node(layer->clip_tree_index());
-       clip_node->id > 1; clip_node = clip_tree.parent(clip_node)) {
+       clip_node->id > ClipTree::kViewportNodeId;
+       clip_node = clip_tree.parent(clip_node)) {
     if (clip_node->applies_local_clip) {
       const TransformNode* transform_node =
           transform_tree.Node(clip_node->target_transform_id);
@@ -1678,10 +1680,11 @@ static bool PointIsClippedByAncestorClipNode(
 
       const LayerImpl* target_layer =
           layer->layer_tree_impl()->LayerById(transform_node->owner_id);
-      DCHECK(transform_node->id == 0 || target_layer->render_surface() ||
+      DCHECK(transform_node->id == TransformTree::kDeviceNodeId ||
+             target_layer->render_surface() ||
              layer->layer_tree_impl()->is_in_resourceless_software_draw_mode());
       gfx::Transform surface_screen_space_transform =
-          transform_node->id == 0 ||
+          transform_node->id == TransformTree::kDeviceNodeId ||
                   (layer->layer_tree_impl()
                        ->is_in_resourceless_software_draw_mode())
               ? gfx::Transform()