cc : Replace LayerImpl::children calls with LayerById

cc/trees/layer_tree_host_unittest_video.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/trees/layer_tree_host.h"
 
 #include "cc/layers/render_surface_impl.h"
 #include "cc/layers/video_layer.h"
 #include "cc/layers/video_layer_impl.h"
 #include "cc/test/fake_video_frame_provider.h"
@@ skipping 14 matching lines @@
     scoped_refptr<Layer> root = Layer::Create();
     root->SetBounds(gfx::Size(10, 10));
     root->SetIsDrawable(true);
 
     scoped_refptr<VideoLayer> video =
         VideoLayer::Create(&video_frame_provider_, media::VIDEO_ROTATION_90);
     video->SetPosition(gfx::PointF(3.f, 3.f));
     video->SetBounds(gfx::Size(4, 5));
     video->SetIsDrawable(true);
     root->AddChild(video);
+    video_layer_id_ = video->id();
 
     layer_tree_host()->SetRootLayer(root);
     layer_tree_host()->SetDeviceScaleFactor(2.f);
     LayerTreeHostVideoTest::SetupTree();
   }
 
   void BeginTest() override {
     num_draws_ = 0;
     PostSetNeedsCommitToMainThread();
   }
@@ skipping 17 matching lines @@
         EndTest();
         break;
     }
 
     EXPECT_EQ(DRAW_SUCCESS, draw_result);
     return draw_result;
   }
 
   void DrawLayersOnThread(LayerTreeHostImpl* host_impl) override {
     VideoLayerImpl* video = static_cast<VideoLayerImpl*>(
-        host_impl->active_tree()->root_layer()->children()[0]);
+        host_impl->active_tree()->LayerById(video_layer_id_));
 
     EXPECT_EQ(media::VIDEO_ROTATION_90, video->video_rotation());
 
     if (num_draws_ == 0)
       video->SetNeedsRedraw();
 
     ++num_draws_;
   }
 
   void AfterTest() override { EXPECT_EQ(2, num_draws_); }
 
  private:
   int num_draws_;
+  int video_layer_id_;
 
   FakeVideoFrameProvider video_frame_provider_;
 };
 
 SINGLE_AND_MULTI_THREAD_TEST_F(LayerTreeHostVideoTestSetNeedsDisplay);
 
 }  // namespace
 }  // namespace cc