ui: Cleanup class/struct forward declarations

cc/trees/occlusion_tracker_unittest.cc

Index: cc/trees/occlusion_tracker_unittest.cc
diff --git a/cc/trees/occlusion_tracker_unittest.cc b/cc/trees/occlusion_tracker_unittest.cc
index 7f8ee8460b1a79d08f325c690f13a991ca2b5ea0..d99d41eb419e31bdbdd40c0511e69b6e85b8b5c2 100644
--- a/cc/trees/occlusion_tracker_unittest.cc
+++ b/cc/trees/occlusion_tracker_unittest.cc
@@ -6,6 +6,7 @@
 
 #include <stddef.h>
 
+#include "cc/animation/animation_host.h"
 #include "cc/base/math_util.h"
 #include "cc/layers/layer.h"
 #include "cc/layers/layer_impl.h"
@@ -87,7 +88,10 @@ class OcclusionTrackerTest : public testing::Test {
  protected:
   explicit OcclusionTrackerTest(bool opaque_layers)
       : opaque_layers_(opaque_layers),
-        host_(FakeLayerTreeHost::Create(&client_, &task_graph_runner_)),
+        animation_host_(AnimationHost::CreateForTesting(ThreadInstance::MAIN)),
+        host_(FakeLayerTreeHost::Create(&client_,
+                                        &task_graph_runner_,
+                                        animation_host_.get())),
         next_layer_impl_id_(1) {}
 
   virtual void RunMyTest() = 0;
@@ -290,6 +294,7 @@ class OcclusionTrackerTest : public testing::Test {
   bool opaque_layers_;
   FakeLayerTreeHostClient client_;
   TestTaskGraphRunner task_graph_runner_;
+  std::unique_ptr<AnimationHost> animation_host_;
   std::unique_ptr<FakeLayerTreeHost> host_;
   // These hold ownership of the layers for the duration of the test.
   LayerImplList render_surface_layer_list_impl_;