Mojo C++ bindings: better log messages for some validation errors at the receiver side.

mojo/public/cpp/bindings/lib/validation_errors.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_VALIDATION_ERRORS_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_LIB_VALIDATION_ERRORS_H_
 
 #include "mojo/public/cpp/system/macros.h"
 
 namespace mojo {
@@ skipping 30 matching lines @@
   VALIDATION_ERROR_UNEXPECTED_NULL_POINTER,
   // |flags| in the message header is an invalid flag combination.
   VALIDATION_ERROR_MESSAGE_HEADER_INVALID_FLAG_COMBINATION,
   // |flags| in the message header indicates that a request ID is required but
   // there isn't one.
   VALIDATION_ERROR_MESSAGE_HEADER_MISSING_REQUEST_ID,
 };
 
 const char* ValidationErrorToString(ValidationError error);
 
-void ReportValidationError(ValidationError error);
+void ReportValidationError(ValidationError error,
+                           const char* description = NULL);
 
 // Only used by validation tests and when there is only one thread doing message
 // validation.
 class ValidationErrorObserverForTesting {
  public:
   ValidationErrorObserverForTesting();
   ~ValidationErrorObserverForTesting();
 
   ValidationError last_error() const { return last_error_; }
   void set_last_error(ValidationError error) { last_error_ = error; }
@@ skipping 39 matching lines @@
 //
 // In non-debug build, does nothing (not even compiling |condition|).
 #define MOJO_INTERNAL_DLOG_SERIALIZATION_WARNING( \
     condition, error, description) \
   MOJO_DLOG_IF(FATAL, (condition) && !ReportSerializationWarning(error)) \
       << "The outgoing message will trigger " \
       << ValidationErrorToString(error) << " at the receiving side (" \
       << description << ").";
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_VALIDATION_ERRORS_H_