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

cc/trees/layer_tree_host_impl.cc

 // Copyright 2011 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/trees/layer_tree_host_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 2545 matching lines @@
   DCHECK(scroll_on_main_thread);
   DCHECK(main_thread_scrolling_reasons);
   *main_thread_scrolling_reasons =
       MainThreadScrollingReason::kNotScrollingOnMain;
 
   // Walk up the hierarchy and look for a scrollable layer.
   LayerImpl* potentially_scrolling_layer_impl = NULL;
   if (layer_impl) {
     ScrollTree& scroll_tree = active_tree_->property_trees()->scroll_tree;
     ScrollNode* scroll_node = scroll_tree.Node(layer_impl->scroll_tree_index());
-    for (; scroll_tree.parent(scroll_node);
-         scroll_node = scroll_tree.parent(scroll_node)) {
+    for (; scroll_node; scroll_node = scroll_tree.parent(scroll_node)) {
       // The content layer can also block attempts to scroll outside the main
       // thread.
       ScrollStatus status =
           TryScroll(device_viewport_point, type, scroll_tree, scroll_node);
       if (status.thread == SCROLL_ON_MAIN_THREAD) {
         if (!!scroll_node->data.main_thread_scrolling_reasons) {
           DCHECK(MainThreadScrollingReason::MainThreadCanSetScrollReasons(
               status.main_thread_scrolling_reasons));
         } else {
           DCHECK(MainThreadScrollingReason::CompositorCanSetScrollReasons(
@@ skipping 1451 matching lines @@
     const {
   return fixed_raster_scale_attempted_scale_change_history_.count() >=
          kFixedRasterScaleAttemptedScaleChangeThreshold;
 }
 
 void LayerTreeHostImpl::SetFixedRasterScaleAttemptedToChangeScale() {
   fixed_raster_scale_attempted_scale_change_history_.set(0);
 }
 
 }  // namespace cc