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

cc/trees/layer_tree_host_unittest.cc

Index: cc/trees/layer_tree_host_unittest.cc
diff --git a/cc/trees/layer_tree_host_unittest.cc b/cc/trees/layer_tree_host_unittest.cc
index bd303e3fae4189621c7725d230ce2f3273fd2fce..a6facc6b8484cdc072c06e7cbd0156b81c0ac8c5 100644
--- a/cc/trees/layer_tree_host_unittest.cc
+++ b/cc/trees/layer_tree_host_unittest.cc
@@ -1774,16 +1774,13 @@ class LayerTreeHostTestDeviceScaleFactorScalesViewportAndLayers
     // Device scale factor should come over to impl.
     EXPECT_NEAR(impl->active_tree()->device_scale_factor(), 1.5f, 0.00001f);
 
-    // Both layers are on impl.
-    ASSERT_EQ(1u, impl->active_tree()->root_layer()->children().size());
-
     // Device viewport is scaled.
     EXPECT_EQ(gfx::Size(60, 60), impl->DrawViewportSize());
 
     FakePictureLayerImpl* root =
         static_cast<FakePictureLayerImpl*>(impl->active_tree()->root_layer());
     FakePictureLayerImpl* child = static_cast<FakePictureLayerImpl*>(
-        impl->active_tree()->root_layer()->children()[0]);
+        impl->active_tree()->LayerById(child_layer_->id()));
 
     // Positions remain in layout pixels.
     EXPECT_EQ(gfx::PointF(), root->position());
@@ -2871,90 +2868,84 @@ class LayerTreeHostTestImplLayersPushProperties
         ++expected_push_properties_grandchild2_impl_;
         break;
       case 6:
-        // First child is removed. Structure of the tree changes here so swap
-        // some of the values. child_impl becomes child2_impl.
-        expected_push_properties_child_impl_ =
-            expected_push_properties_child2_impl_;
-        expected_push_properties_child2_impl_ = 0;
-        // grandchild_impl becomes grandchild2_impl.
-        expected_push_properties_grandchild_impl_ =
-            expected_push_properties_grandchild2_impl_;
-        expected_push_properties_grandchild2_impl_ = 0;
+        // First child is removed. Structure of the tree changes.
+        expected_push_properties_child_impl_ = 0;
+        expected_push_properties_grandchild_impl_ = 0;
 
-        // grandchild_impl is now the leaf that always pushes. It is pushed.
-        ++expected_push_properties_grandchild_impl_;
+        // The leaf that always pushes is pushed.
+        ++expected_push_properties_grandchild2_impl_;
         break;
       case 7:
         // The leaf that always pushes is pushed.
-        ++expected_push_properties_grandchild_impl_;
+        ++expected_push_properties_grandchild2_impl_;
 
         // Child is added back. New layers are initialized.
-        ++expected_push_properties_grandchild2_impl_;
-        ++expected_push_properties_child2_impl_;
+        ++expected_push_properties_grandchild_impl_;
+        ++expected_push_properties_child_impl_;
         break;
       case 8:
         // Leaf is removed.
-        expected_push_properties_grandchild2_impl_ = 0;
+        expected_push_properties_grandchild_impl_ = 0;
 
         // Always pushing.
-        ++expected_push_properties_grandchild_impl_;
+        ++expected_push_properties_grandchild2_impl_;
         break;
       case 9:
         // Leaf is added back
-        ++expected_push_properties_grandchild2_impl_;
+        ++expected_push_properties_grandchild_impl_;
 
         // The leaf that always pushes is pushed.
-        ++expected_push_properties_grandchild_impl_;
+        ++expected_push_properties_grandchild2_impl_;
         break;
       case 10:
         // The leaf that always pushes is pushed.
-        ++expected_push_properties_grandchild_impl_;
+        ++expected_push_properties_grandchild2_impl_;
         break;
       case 11:
         // The leaf that always pushes is pushed.
-        ++expected_push_properties_grandchild_impl_;
+        ++expected_push_properties_grandchild2_impl_;
         break;
       case 12:
         // The leaf that always pushes is pushed.
-        ++expected_push_properties_grandchild_impl_;
+        ++expected_push_properties_grandchild2_impl_;
 
         // This child position was changed. So the subtree needs to push
         // properties.
-        ++expected_push_properties_child2_impl_;
-        ++expected_push_properties_grandchild2_impl_;
+        ++expected_push_properties_child_impl_;
+        ++expected_push_properties_grandchild_impl_;
         break;
       case 13:
         // The position of this child was changed.
-        ++expected_push_properties_child_impl_;
+        ++expected_push_properties_child2_impl_;
 
         // The leaf that always pushes is pushed.
-        ++expected_push_properties_grandchild_impl_;
+        ++expected_push_properties_grandchild2_impl_;
         break;
       case 14:
         // Second child is removed from tree. Don't discard counts because
         // they are added back before commit.
 
         // The leaf that always pushes is pushed.
-        ++expected_push_properties_grandchild_impl_;
+        ++expected_push_properties_grandchild2_impl_;
 
         // Second child added back.
-        ++expected_push_properties_child2_impl_;
-        ++expected_push_properties_grandchild2_impl_;
+        ++expected_push_properties_child_impl_;
+        ++expected_push_properties_grandchild_impl_;
 
         break;
       case 15:
         // The position of this child was changed.
-        ++expected_push_properties_grandchild2_impl_;
+        ++expected_push_properties_grandchild_impl_;
 
         // The leaf that always pushes is pushed.
-        ++expected_push_properties_grandchild_impl_;
+        ++expected_push_properties_grandchild2_impl_;
         break;
       case 16:
         // Second child is invalidated with SetNeedsDisplay
-        ++expected_push_properties_child2_impl_;
+        ++expected_push_properties_child_impl_;
 
         // The leaf that always pushed is pushed.
-        ++expected_push_properties_grandchild_impl_;
+        ++expected_push_properties_grandchild2_impl_;
         break;
     }
 
@@ -2969,23 +2960,24 @@ class LayerTreeHostTestImplLayersPushProperties
     root_impl_ = static_cast<PushPropertiesCountingLayerImpl*>(
         host_impl->RootLayer());
 
-    if (root_impl_ && root_impl_->children().size() > 0) {
+    LayerTreeImpl* impl = root_impl_->layer_tree_impl();
+    if (impl->LayerById(child_->id())) {
       child_impl_ = static_cast<PushPropertiesCountingLayerImpl*>(
-          root_impl_->children()[0]);
+          impl->LayerById(child_->id()));
 
-      if (child_impl_ && child_impl_->children().size() > 0)
+      if (impl->LayerById(grandchild_->id()))
         grandchild_impl_ = static_cast<PushPropertiesCountingLayerImpl*>(
-            child_impl_->children()[0]);
+            impl->LayerById(grandchild_->id()));
     }
 
-    if (root_impl_ && root_impl_->children().size() > 1) {
+    if (impl->LayerById(child2_->id())) {
       child2_impl_ = static_cast<PushPropertiesCountingLayerImpl*>(
-          root_impl_->children()[1]);
+          impl->LayerById(child2_->id()));
 
-      if (child2_impl_ && child2_impl_->children().size() > 0)
+      if (impl->LayerById(leaf_always_pushing_layer_->id()))
         leaf_always_pushing_layer_impl_ =
             static_cast<PushPropertiesCountingLayerImpl*>(
-                child2_impl_->children()[0]);
+                impl->LayerById(leaf_always_pushing_layer_->id()));
     }
 
     if (root_impl_)
@@ -3702,9 +3694,7 @@ class LayerTreeHostTestPushHiddenLayer : public LayerTreeHostTest {
   }
 
   void DidActivateTreeOnThread(LayerTreeHostImpl* impl) override {
-    LayerImpl* root = impl->active_tree()->root_layer();
-    LayerImpl* parent = root->children()[0];
-    LayerImpl* child = parent->children()[0];
+    LayerImpl* child = impl->active_tree()->LayerById(child_layer_->id());
 
     switch (impl->active_tree()->source_frame_number()) {
       case 1: