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

cc/trees/layer_tree_host_unittest_damage.cc

Index: cc/trees/layer_tree_host_unittest_damage.cc
diff --git a/cc/trees/layer_tree_host_unittest_damage.cc b/cc/trees/layer_tree_host_unittest_damage.cc
index 76c26f6682e9c35bf8fdbf75506167a702213575..522a2f1578b15213b0132b71125db7dd27974dff 100644
--- a/cc/trees/layer_tree_host_unittest_damage.cc
+++ b/cc/trees/layer_tree_host_unittest_damage.cc
@@ -339,6 +339,7 @@ class LayerTreeHostScrollbarDamageTest : public LayerTreeHostDamageTest {
 
     scoped_refptr<Layer> scroll_clip_layer = Layer::Create();
     scoped_refptr<Layer> content_layer = FakePictureLayer::Create(&client_);
+    content_layer_ = content_layer.get();
     content_layer->SetScrollClipLayerId(scroll_clip_layer->id());
     content_layer->SetScrollOffset(gfx::ScrollOffset(10, 20));
     content_layer->SetBounds(gfx::Size(100, 200));
@@ -368,6 +369,9 @@ class LayerTreeHostScrollbarDamageTest : public LayerTreeHostDamageTest {
 
  private:
   FakeContentLayerClient client_;
+
+ protected:
+  Layer* content_layer_;

[ajuma, 2016/04/20 21:40:52]

This should be a scoped_refptr.

[sunxd, 2016/04/21 17:31:15]

Done.

 };
 
 class LayerTreeHostDamageTestScrollbarDoesDamage
@@ -410,9 +414,8 @@ class LayerTreeHostDamageTestScrollbarDoesDamage
   void SwapBuffersOnThread(LayerTreeHostImpl* host_impl, bool result) override {
     ++did_swaps_;
     EXPECT_TRUE(result);
-    LayerImpl* root = host_impl->active_tree()->root_layer();
-    LayerImpl* scroll_clip_layer = root->children()[0];
-    LayerImpl* scroll_layer = scroll_clip_layer->children()[0];
+    LayerImpl* scroll_layer =
+        host_impl->active_tree()->LayerById(content_layer_->id());
     switch (did_swaps_) {
       case 1:
         // Test that modifying the position of the content layer (not
@@ -439,18 +442,13 @@ class LayerTreeHostDamageTestScrollbarDoesDamage
 
   void ModifyContentLayerPosition() {
     EXPECT_EQ(1, did_swaps_);
-    Layer* root = layer_tree_host()->root_layer();
-    Layer* scroll_clip_layer = root->child_at(0);
-    Layer* scroll_layer = scroll_clip_layer->child_at(0);
-    scroll_layer->SetPosition(gfx::PointF(10.f, 10.f));
+    content_layer_->SetPosition(gfx::PointF(10.f, 10.f));
   }
 
   void ResizeScrollLayer() {
     EXPECT_EQ(3, did_swaps_);
     Layer* root = layer_tree_host()->root_layer();
-    Layer* scroll_clip_layer = root->child_at(0);
-    Layer* scroll_layer = scroll_clip_layer->child_at(0);
-    scroll_layer->SetBounds(
+    content_layer_->SetBounds(
         gfx::Size(root->bounds().width() + 60, root->bounds().height() + 100));
   }
 
@@ -503,9 +501,8 @@ class LayerTreeHostDamageTestScrollbarCommitDoesNoDamage
   void SwapBuffersOnThread(LayerTreeHostImpl* host_impl, bool result) override {
     ++did_swaps_;
     EXPECT_TRUE(result);
-    LayerImpl* root = host_impl->active_tree()->root_layer();
-    LayerImpl* scroll_clip_layer = root->children()[0];
-    LayerImpl* scroll_layer = scroll_clip_layer->children()[0];
+    LayerImpl* scroll_layer =
+        host_impl->active_tree()->LayerById(content_layer_->id());
     switch (did_swaps_) {
       case 1:
         // Scroll on the thread.  This should damage the scrollbar for the