cc : Replace LayerImpl::children calls with LayerById

cc/layers/texture_layer_unittest.cc

 // Copyright 2012 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/layers/texture_layer.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 1311 matching lines @@
 
   void SetupTree() override {
     LayerTreeTest::SetupTree();
 
     scoped_refptr<TextureLayer> texture_layer =
         TextureLayer::CreateForMailbox(this);
     texture_layer->SetBounds(gfx::Size(10, 10));
     texture_layer->SetIsDrawable(true);
 
     layer_tree_host()->root_layer()->AddChild(texture_layer);
+    texture_layer_id_ = texture_layer->id();
   }
 
   void BeginTest() override {
     mailbox_released_ = false;
     PostSetNeedsCommitToMainThread();
   }
 
   void DidCommitAndDrawFrame() override { EndTest(); }
 
   void AfterTest() override { EXPECT_TRUE(mailbox_released_); }
 
+ protected:
+  int texture_layer_id_;
+
  private:
   bool mailbox_released_;
 };
 
 class TextureLayerReleaseResourcesAfterCommit
     : public TextureLayerReleaseResourcesBase {
  public:
   void CommitCompleteOnThread(LayerTreeHostImpl* host_impl) override {
     LayerTreeImpl* tree = nullptr;
     tree = host_impl->sync_tree();
-    tree->root_layer()->children()[0]->ReleaseResources();
+    tree->LayerById(texture_layer_id_)->ReleaseResources();
   }
 };
 
 SINGLE_AND_MULTI_THREAD_TEST_F(TextureLayerReleaseResourcesAfterCommit);
 
 class TextureLayerReleaseResourcesAfterActivate
     : public TextureLayerReleaseResourcesBase {
  public:
   void DidActivateTreeOnThread(LayerTreeHostImpl* host_impl) override {
-    host_impl->active_tree()->root_layer()->children()[0]->ReleaseResources();
+    host_impl->active_tree()->LayerById(texture_layer_id_)->ReleaseResources();
   }
 };
 
 SINGLE_AND_MULTI_THREAD_TEST_F(TextureLayerReleaseResourcesAfterActivate);
 
 class TextureLayerWithMailboxMainThreadDeleted : public LayerTreeTest {
  public:
   void ReleaseCallback(const gpu::SyncToken& sync_token, bool lost_resource) {
     EXPECT_EQ(true, main_thread_.CalledOnValidThread());
     EXPECT_FALSE(lost_resource);
@@ skipping 132 matching lines @@
   int callback_count_;
   scoped_refptr<Layer> root_;
   scoped_refptr<TextureLayer> layer_;
 };
 
 SINGLE_AND_MULTI_THREAD_DIRECT_RENDERER_TEST_F(
     TextureLayerWithMailboxImplThreadDeleted);
 
 }  // namespace
 }  // namespace cc