Mojo: Report bindings validation errors via MojoNotifyBadMessage

mojo/public/cpp/bindings/lib/message_header_validator.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_HEADER_VALIDATOR_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_LIB_MESSAGE_HEADER_VALIDATOR_H_
 
 #include "mojo/public/cpp/bindings/message.h"
 #include "mojo/public/cpp/bindings/message_filter.h"
 
 namespace mojo {
 namespace internal {
 
 class MessageHeaderValidator : public MessageFilter {
  public:
   explicit MessageHeaderValidator(MessageReceiver* sink = nullptr);
+  MessageHeaderValidator(const std::string& description,
+                         MessageReceiver* sink = nullptr);
+
+  // Sets the description associated with this validator. Used for reporting
+  // more detailed validation errors.
+  void SetDescription(const std::string& description);
 
   bool Accept(Message* message) override;
+
+ private:
+  std::string description_;
 };
 
 }  // namespace internal
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_MESSAGE_HEADER_VALIDATOR_H_