Fix unused variables errors in cc/.

cc/animation/animation_host.cc

Index: cc/animation/animation_host.cc
diff --git a/cc/animation/animation_host.cc b/cc/animation/animation_host.cc
index 489c6f8d66153d7febd7e6509090318b7acf4607..82a5e722c3230f4e4ebeb6dfaa9785282330187f 100644
--- a/cc/animation/animation_host.cc
+++ b/cc/animation/animation_host.cc
@@ -14,15 +14,13 @@
 
 namespace cc {
 
-scoped_ptr<AnimationHost> AnimationHost::Create(
-    ThreadInstance thread_instance) {
-  return make_scoped_ptr(new AnimationHost(thread_instance));
+scoped_ptr<AnimationHost> AnimationHost::Create() {
+  return make_scoped_ptr(new AnimationHost);
 }
 
-AnimationHost::AnimationHost(ThreadInstance thread_instance)
+AnimationHost::AnimationHost()
     : animation_registrar_(AnimationRegistrar::Create()),
-      mutator_host_client_(),
-      thread_instance_(thread_instance) {
+      mutator_host_client_(nullptr) {
 }
 
 AnimationHost::~AnimationHost() {