cc: Remove LayerImpl::children() calls after tree synchronization

cc/trees/damage_tracker_unittest.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/damage_tracker.h"
 
 #include <stddef.h>
 
 #include "cc/base/math_util.h"
 #include "cc/layers/layer_impl.h"
@@ skipping 24 matching lines @@
 
   FakeLayerTreeHostImpl::RecursiveUpdateNumChildren(root);
   root->layer_tree_impl()->IncrementRenderSurfaceListIdForTesting();
   LayerTreeHostCommon::CalcDrawPropsImplInputsForTesting inputs(
       root, root->bounds(), render_surface_layer_list,
       root->layer_tree_impl()->current_render_surface_list_id());
   LayerTreeHostCommon::CalculateDrawProperties(&inputs);
   ASSERT_TRUE(root->render_surface());
 }
 
-void ClearDamageForAllSurfaces(LayerImpl* layer) {
-  if (layer->render_surface())
-    layer->render_surface()->damage_tracker()->DidDrawDamagedArea();
-
-  // Recursively clear damage for any existing surface.
-  for (size_t i = 0; i < layer->children().size(); ++i)
-    ClearDamageForAllSurfaces(layer->children()[i]);
+void ClearDamageForAllSurfaces(LayerImpl* root) {
+  for (auto* layer : *root->layer_tree_impl()) {
+    if (layer->render_surface())
+      layer->render_surface()->damage_tracker()->DidDrawDamagedArea();
+  }
 }
 
 void EmulateDrawingOneFrame(LayerImpl* root) {
   // This emulates only steps that are relevant to testing the damage tracker:
   //   1. computing the render passes and layerlists
   //   2. updating all damage trackers in the correct order
   //   3. resetting all update_rects and property_changed flags for all layers
   //      and surfaces.
 
   LayerImplList render_surface_layer_list;
@@ skipping 1492 matching lines @@
     gfx::Rect root_damage_rect =
         root->render_surface()->damage_tracker()->current_damage_rect();
     gfx::Rect damage_we_care_about = gfx::Rect(i, i);
     EXPECT_LE(damage_we_care_about.right(), root_damage_rect.right());
     EXPECT_LE(damage_we_care_about.bottom(), root_damage_rect.bottom());
   }
 }
 
 }  // namespace
 }  // namespace cc