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

mojo/public/cpp/bindings/lib/validation_errors.cc

 // 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.
 
 #include "mojo/public/cpp/bindings/lib/validation_errors.h"
 
 #include "mojo/public/cpp/environment/logging.h"
 
 namespace mojo {
 namespace internal {
@@ skipping 26 matching lines @@
       return "VALIDATION_ERROR_UNEXPECTED_NULL_POINTER";
     case VALIDATION_ERROR_MESSAGE_HEADER_INVALID_FLAG_COMBINATION:
       return "VALIDATION_ERROR_MESSAGE_HEADER_INVALID_FLAG_COMBINATION";
     case VALIDATION_ERROR_MESSAGE_HEADER_MISSING_REQUEST_ID:
       return "VALIDATION_ERROR_MESSAGE_HEADER_MISSING_REQUEST_ID";
   }
 
   return "Unknown error";
 }
 
-void ReportValidationError(ValidationError error) {
-  if (g_validation_error_observer)
+void ReportValidationError(ValidationError error, const char* description) {
+  if (g_validation_error_observer) {
     g_validation_error_observer->set_last_error(error);
-  else
+  } else if (description) {
+    MOJO_LOG(ERROR) << "Invalid message: " << ValidationErrorToString(error)
+                    << " (" << description << ")";
+  } else {
     MOJO_LOG(ERROR) << "Invalid message: " << ValidationErrorToString(error);
+  }
 }
 
 ValidationErrorObserverForTesting::ValidationErrorObserverForTesting()
     : last_error_(VALIDATION_ERROR_NONE) {
   MOJO_DCHECK(!g_validation_error_observer);
   g_validation_error_observer = this;
 }
 
 ValidationErrorObserverForTesting::~ValidationErrorObserverForTesting() {
   MOJO_DCHECK(g_validation_error_observer == this);
@@ skipping 16 matching lines @@
 }
 
 SerializationWarningObserverForTesting::
 ~SerializationWarningObserverForTesting() {
   MOJO_DCHECK(g_serialization_warning_observer == this);
   g_serialization_warning_observer = NULL;
 }
 
 }  // namespace internal
 }  // namespace mojo