Add FlushForTesting to InterfacePtr and Binding.

mojo/public/cpp/bindings/lib/control_message_proxy.h

Index: mojo/public/cpp/bindings/lib/control_message_proxy.h
diff --git a/mojo/public/cpp/bindings/lib/control_message_proxy.h b/mojo/public/cpp/bindings/lib/control_message_proxy.h
index 5ec6ddca351e7ce675cb143b3fe0a77c406d2f90..c3260d1095f9dc65d8f9b82f551696af1be52627 100644
--- a/mojo/public/cpp/bindings/lib/control_message_proxy.h
+++ b/mojo/public/cpp/bindings/lib/control_message_proxy.h
@@ -7,7 +7,7 @@
 
 #include <stdint.h>
 
-#include "base/callback_forward.h"
+#include "base/callback.h"
 #include "base/macros.h"
 #include "mojo/public/cpp/bindings/lib/serialization_context.h"
 
@@ -22,14 +22,24 @@ class ControlMessageProxy {
  public:
   // Doesn't take ownership of |receiver|. It must outlive this object.
   explicit ControlMessageProxy(MessageReceiverWithResponder* receiver);
+  ~ControlMessageProxy();
 
   void QueryVersion(const base::Callback<void(uint32_t)>& callback);
   void RequireVersion(uint32_t version);
 
- protected:
+  void FlushForTesting();
+
+  void OnConnectionError();
+
+ private:
+  void RunFlushForTestingClosure();
+
   // Not owned.
   MessageReceiverWithResponder* receiver_;
   SerializationContext context_;
+  bool encountered_error_ = false;
+
+  base::Closure run_loop_quit_closure_;
 
   DISALLOW_COPY_AND_ASSIGN(ControlMessageProxy);
 };