Mojo C++ bindings: better log message for serialization warnings.

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

Index: mojo/public/cpp/bindings/lib/validation_errors.h
diff --git a/mojo/public/cpp/bindings/lib/validation_errors.h b/mojo/public/cpp/bindings/lib/validation_errors.h
index d7e651a9f391aad4f91c6a2ab3b520bdcf426d7f..8ca0eae74b1dba39bff287d47d275ead14fdd6cd 100644
--- a/mojo/public/cpp/bindings/lib/validation_errors.h
+++ b/mojo/public/cpp/bindings/lib/validation_errors.h
@@ -100,9 +100,11 @@ class SerializationWarningObserverForTesting {
 // of the serialzation result.
 //
 // In non-debug build, does nothing (not even compiling |condition|).
-#define MOJO_INTERNAL_DLOG_SERIALIZATION_WARNING(condition, error) \
-    MOJO_DLOG_IF(FATAL, (condition) && !ReportSerializationWarning(error)) \
-        << "The outgoing message will trigger " \
-        << ValidationErrorToString(error) << " at the receiving side.";
+#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_