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

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

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MOJO_PUBLIC_CPP_BINDINGS_LIB_MESSAGE_INTERNAL_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_LIB_MESSAGE_INTERNAL_H_
 
 #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)
 
 struct MessageHeader : internal::StructHeader {
   // Interface ID for identifying multiple interfaces running on the same
   // message pipe.
   uint32_t interface_id;
   // Message name, which is scoped to the interface that the message belongs to.
   uint32_t name;
   // 0 or either of the enum values defined above.
   uint32_t flags;
   // Unused padding to make the struct size a multiple of 8 bytes.
   uint32_t padding;
 };
 static_assert(sizeof(MessageHeader) == 24, "Bad sizeof(MessageHeader)");
 
 struct MessageHeaderWithRequestID : MessageHeader {
   // Only used if either kFlagExpectsResponse or kFlagIsResponse is set in
   // order to match responses with corresponding requests.
   uint64_t request_id;
 };
 static_assert(sizeof(MessageHeaderWithRequestID) == 32,
               "Bad sizeof(MessageHeaderWithRequestID)");
 
 #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
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_MESSAGE_INTERNAL_H_