Avoid double task trampoline for Pipeline state transitions.

media/mojo/services/mojo_renderer_impl.cc

Index: media/mojo/services/mojo_renderer_impl.cc
diff --git a/media/mojo/services/mojo_renderer_impl.cc b/media/mojo/services/mojo_renderer_impl.cc
index 8adc9a65c0edac2a144d1ebc417c93ecab277253..e085521dee4893adc0d965c18674d6ae9d2c37b9 100644
--- a/media/mojo/services/mojo_renderer_impl.cc
+++ b/media/mojo/services/mojo_renderer_impl.cc
@@ -56,7 +56,7 @@ void MojoRendererImpl::Initialize(
 
   demuxer_stream_provider_ = demuxer_stream_provider;
   // |init_cb| can be called on other thread.
-  init_cb_ = init_cb;
+  init_cb_ = BindToCurrentLoop(init_cb);
   ended_cb_ = ended_cb;
   error_cb_ = error_cb;
   buffering_state_cb_ = buffering_state_cb;