Introduce command buffer control thread

mojo/public/cpp/bindings/binding.h

Index: mojo/public/cpp/bindings/binding.h
diff --git a/mojo/public/cpp/bindings/binding.h b/mojo/public/cpp/bindings/binding.h
index 080d62eebd87d012615476ee60b1a41944bd21f4..72dbde302253425a08c9943fe52fc8bb906b1ef9 100644
--- a/mojo/public/cpp/bindings/binding.h
+++ b/mojo/public/cpp/bindings/binding.h
@@ -122,6 +122,9 @@ class Binding : public ErrorHandler {
 
   Interface* impl() { return impl_; }
   Client* client() { return proxy_; }
+
+  bool is_bound() const { return !!internal_router_; }
+
   // Exposed for testing, should not generally be used.
   internal::Router* internal_router() { return internal_router_; }