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

cc/trees/layer_tree_host_impl_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/layer_tree_host_impl.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <cmath>
@@ skipping 211 matching lines @@
   }
 
   static gfx::Vector2dF ScrollDelta(LayerImpl* layer_impl) {
     gfx::ScrollOffset delta =
         layer_impl->layer_tree_impl()
             ->property_trees()
             ->scroll_tree.GetScrollOffsetDeltaForTesting(layer_impl->id());
     return gfx::Vector2dF(delta.x(), delta.y());
   }
 
-  static void ExpectClearedScrollDeltasRecursive(LayerImpl* layer) {
-    ASSERT_EQ(ScrollDelta(layer), gfx::Vector2d());
-    for (size_t i = 0; i < layer->children().size(); ++i)
-      ExpectClearedScrollDeltasRecursive(layer->children()[i]);
+  static void ExpectClearedScrollDeltasRecursive(LayerImpl* root) {
+    for (auto* layer : *root->layer_tree_impl())
+      ASSERT_EQ(ScrollDelta(layer), gfx::Vector2d());
   }
 
   static ::testing::AssertionResult ScrollInfoContains(
       const ScrollAndScaleSet& scroll_info,
       int id,
       const gfx::Vector2d& scroll_delta) {
     int times_encountered = 0;
 
     for (size_t i = 0; i < scroll_info.scrolls.size(); ++i) {
       if (scroll_info.scrolls[i].layer_id != id)
@@ skipping 10423 matching lines @@
     // There should not be any jitter measured till we hit the fixed point hits
     // threshold.
     float expected_jitter =
         (i == pending_tree->kFixedPointHitsThreshold) ? 500 : 0;
     EXPECT_EQ(jitter, expected_jitter);
   }
 }
 
 }  // namespace
 }  // namespace cc