Revert "Shouldn't access LayerTreeTest::layer_tree_host on impl thread"

cc/trees/layer_tree_host_unittest_animation.cc

Index: cc/trees/layer_tree_host_unittest_animation.cc
diff --git a/cc/trees/layer_tree_host_unittest_animation.cc b/cc/trees/layer_tree_host_unittest_animation.cc
index cf2a42f821f6e75e7dfcf751dd498f6166db8acd..43e0b2a14a1cded2df9f44f0798c542a729caaf2 100644
--- a/cc/trees/layer_tree_host_unittest_animation.cc
+++ b/cc/trees/layer_tree_host_unittest_animation.cc
@@ -291,6 +291,7 @@ class LayerTreeHostAnimationTestTickAnimationWhileBackgrounded
 SINGLE_AND_MULTI_THREAD_TEST_F(
     LayerTreeHostAnimationTestTickAnimationWhileBackgrounded);
 
+// Ensures that animations continue to be ticked when we are backgrounded.
 class LayerTreeHostAnimationTestAddAnimationWithTimingFunction
     : public LayerTreeHostAnimationTest {
  public:
@@ -300,7 +301,6 @@ class LayerTreeHostAnimationTestAddAnimationWithTimingFunction
     LayerTreeHostAnimationTest::SetupTree();
     content_ = FakeContentLayer::Create(&client_);
     content_->SetBounds(gfx::Size(4, 4));
-    content_->set_layer_animation_delegate(this);
     layer_tree_host()->root_layer()->AddChild(content_);
   }
 
@@ -308,12 +308,17 @@ class LayerTreeHostAnimationTestAddAnimationWithTimingFunction
     PostAddAnimationToMainThread(content_);
   }
 
-  virtual void notifyAnimationStarted(double wallClockTime) OVERRIDE {
+  virtual void AnimateLayers(
+      LayerTreeHostImpl* host_impl,
+      base::TimeTicks monotonic_time) OVERRIDE {
     LayerAnimationController* controller =
         layer_tree_host()->root_layer()->children()[0]->
         layer_animation_controller();
     Animation* animation =
         controller->GetAnimation(Animation::Opacity);
+    if (!animation)
+      return;
+
     const FloatAnimationCurve* curve =
         animation->curve()->ToFloatAnimationCurve();
     float start_opacity = curve->GetValue(0.0);
@@ -326,8 +331,14 @@ class LayerTreeHostAnimationTestAddAnimationWithTimingFunction
     // because of the default ease timing function.
     EXPECT_FLOAT_EQ(linearly_interpolated_opacity, curve->GetValue(time));
 
-    controller->RemoveAnimation(animation->id());
+    LayerAnimationController* controller_impl =
+        host_impl->active_tree()->root_layer()->children()[0]->
+        layer_animation_controller();
+    Animation* animation_impl =
+        controller_impl->GetAnimation(Animation::Opacity);
 
+    controller->RemoveAnimation(animation->id());
+    controller_impl->RemoveAnimation(animation_impl->id());
     EndTest();
   }