ui: Cleanup class/struct forward declarations

cc/test/layer_tree_test.h

Index: cc/test/layer_tree_test.h
diff --git a/cc/test/layer_tree_test.h b/cc/test/layer_tree_test.h
index bb0813622a3a0958633c81d5a1f91bc2ef2e9fe2..84491e6572ce7646a07a09834ec5c976f3152843 100644
--- a/cc/test/layer_tree_test.h
+++ b/cc/test/layer_tree_test.h
@@ -18,6 +18,8 @@
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace cc {
+
+class AnimationHost;
 class AnimationPlayer;
 class FakeLayerTreeHostClient;
 class LayerImpl;
@@ -94,6 +96,8 @@ class LayerTreeTest : public testing::Test, public TestHooks {
   void DoBeginTest();
   void Timeout();
 
+  AnimationHost* animation_host() const { return animation_host_.get(); }
+
  protected:
   LayerTreeTest();
 
@@ -179,6 +183,7 @@ class LayerTreeTest : public testing::Test, public TestHooks {
 
   std::unique_ptr<LayerTreeHostClientForTesting> client_;
   std::unique_ptr<LayerTreeHost> layer_tree_host_;
+  std::unique_ptr<AnimationHost> animation_host_;
   LayerTreeHostInProcess* layer_tree_host_in_process_;
 
   bool beginning_ = false;