cc: Remove LayerImpl::children() calls from descendants of LayerTreeTest

cc/trees/layer_tree_host_unittest_copyrequest.cc

 // Copyright 2013 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 <stddef.h>
 
 #include "base/memory/ptr_util.h"
 #include "cc/layers/layer_iterator.h"
 #include "cc/output/copy_output_request.h"
 #include "cc/output/copy_output_result.h"
@@ skipping 460 matching lines @@
 
   void CopyOutputCallback(std::unique_ptr<CopyOutputResult> result) {
     EXPECT_TRUE(layer_tree_host()->task_runner_provider()->IsMainThread());
     EXPECT_EQ(copy_layer_->bounds().ToString(), result->size().ToString());
     EndTest();
   }
 
   void DrawLayersOnThread(LayerTreeHostImpl* host_impl) override {
     Renderer* renderer = host_impl->renderer();
 
-    LayerImpl* root = host_impl->active_tree()->root_layer();
-    LayerImpl* grand_parent = root->children()[0];
-    LayerImpl* parent = grand_parent->children()[0];
-    LayerImpl* copy_layer = parent->children()[0];
+    LayerImpl* parent =
+        host_impl->active_tree()->LayerById(parent_layer_->id());
+    LayerImpl* copy_layer =
+        host_impl->active_tree()->LayerById(copy_layer_->id());
 
     // |parent| owns a surface, but it was hidden and not part of the copy
     // request so it should not allocate any resource.
     EXPECT_FALSE(renderer->HasAllocatedResourcesForTesting(
         parent->render_surface()->GetRenderPassId()));
 
     // |copy_layer| should have been rendered to a texture since it was needed
     // for a copy request.
     if (did_draw_) {
       // TODO(crbug.com/564832): Ignore the extra frame that occurs due to copy
@@ skipping 152 matching lines @@
     PostSetNeedsCommitToMainThread();
 
     // Prevent drawing.
     layer_tree_host()->SetViewportSize(gfx::Size(0, 0));
 
     AddCopyRequest(copy_layer_.get());
   }
 
   void DidActivateTreeOnThread(LayerTreeHostImpl* impl) override {
     if (impl->active_tree()->source_frame_number() == 0) {
-      LayerImpl* root = impl->active_tree()->root_layer();
-      EXPECT_TRUE(root->children()[0]->HasCopyRequest());
+      EXPECT_TRUE(impl->active_tree()->LayerById(copy_layer_->id()));
       saw_copy_request_ = true;
     }
   }
 
   void DidCommit() override {
     if (layer_tree_host()->source_frame_number() == 1) {
       // Allow drawing.
       layer_tree_host()->SetViewportSize(gfx::Size(root_->bounds()));
 
       AddCopyRequest(copy_layer_.get());
@@ skipping 517 matching lines @@
               &LayerTreeHostCopyRequestTestMultipleDrawsHiddenCopyRequest::
                   CopyOutputCallback,
               base::Unretained(this))));
     }
   }
 
   DrawResult PrepareToDrawOnThread(LayerTreeHostImpl* host_impl,
                                    LayerTreeHostImpl::FrameData* frame_data,
                                    DrawResult draw_result) override {
     LayerImpl* root = host_impl->active_tree()->root_layer();
-    LayerImpl* child = root->children()[0];
+    LayerImpl* child = host_impl->active_tree()->LayerById(child_->id());
 
     bool saw_root = false;
     bool saw_child = false;
     for (LayerIterator it =
              LayerIterator::Begin(frame_data->render_surface_layer_list);
          it != LayerIterator::End(frame_data->render_surface_layer_list);
          ++it) {
       if (it.represents_itself()) {
         if (*it == root)
           saw_root = true;
@@ skipping 58 matching lines @@
   int num_draws_;
   bool copy_happened_;
   bool draw_happened_;
 };
 
 SINGLE_AND_MULTI_THREAD_DIRECT_RENDERER_TEST_F(
     LayerTreeHostCopyRequestTestMultipleDrawsHiddenCopyRequest);
 
 }  // namespace
 }  // namespace cc