Mojo C++ Bindings: Add helpers for bad message reporting

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

Index: mojo/public/cpp/bindings/lib/message_internal.h
diff --git a/mojo/public/cpp/bindings/lib/message_internal.h b/mojo/public/cpp/bindings/lib/message_internal.h
index 63edffd7cbdbfff7be3b76cde15e42602c541737..fb606538637cee68b81b6a4b840d264679d1b087 100644
--- a/mojo/public/cpp/bindings/lib/message_internal.h
+++ b/mojo/public/cpp/bindings/lib/message_internal.h
@@ -7,9 +7,13 @@
 
 #include <stdint.h>
 
+#include "base/macros.h"
 #include "mojo/public/cpp/bindings/lib/bindings_internal.h"
 
 namespace mojo {
+
+class Message;
+
 namespace internal {
 
 #pragma pack(push, 1)
@@ -37,6 +41,27 @@ static_assert(sizeof(MessageHeaderWithRequestID) == 32,
 
 #pragma pack(pop)
 
+class MessageDispatchContext {
+ public:
+  explicit MessageDispatchContext(Message* message);
+  ~MessageDispatchContext();
+
+  static MessageDispatchContext* current();
+
+  Message* message() { return message_; }
+
+ private:
+  MessageDispatchContext* outer_context_;
+  Message* message_;
+
+  DISALLOW_COPY_AND_ASSIGN(MessageDispatchContext);
+};
+
+class SyncMessageResponseSetup {
+ public:
+  static void SetCurrentSyncResponseMessage(Message* message);
+};
+
 }  // namespace internal
 }  // namespace mojo