Pass in media message loop to VideoRendererBase and enforce calling on the right thread.

media/base/bind_to_loop.h

Index: media/base/bind_to_loop.h
diff --git a/media/base/bind_to_loop.h b/media/base/bind_to_loop.h
index 013389aa327367a368152fa7aa0dfe696e2739ac..5b9c69423ed091f75559f364d8ff8481a5b88178 100644
--- a/media/base/bind_to_loop.h
+++ b/media/base/bind_to_loop.h
@@ -161,6 +161,13 @@ static base::Callback<T> BindToLoop(
   return base::Bind(&internal::TrampolineHelper<T>::Run, loop, cb);
 }
 
+template<typename T>
+static base::Callback<T> BindToCurrentLoop(
+    const base::Callback<T>& cb) {
+  return base::Bind(&internal::TrampolineHelper<T>::Run,
+                    base::MessageLoopProxy::current(), cb);
+}
+
 }  // namespace media
 
 #endif  // MEDIA_BASE_BIND_TO_LOOP_H_