Move generated Mojo C++ error reporting code out of line

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 ec0aa2798c28c026ff611e6e37de3886133bb353..43db70c91df10b3bb9d79743829c15ef02f51892 100644
--- a/mojo/public/cpp/bindings/lib/validation_errors.h
+++ b/mojo/public/cpp/bindings/lib/validation_errors.h
@@ -11,6 +11,9 @@
 #include "mojo/public/cpp/bindings/lib/validation_context.h"
 
 namespace mojo {
+
+class Message;
+
 namespace internal {
 
 enum ValidationError {
@@ -75,6 +78,11 @@ void ReportValidationError(ValidationContext* context,
                            ValidationError error,
                            const char* description = nullptr);
 
+void ReportValidationErrorForMessage(
+    mojo::Message* message,
+    ValidationError error,
+    const char* description = nullptr);
+
 // Only used by validation tests and when there is only one thread doing message
 // validation.
 class ValidationErrorObserverForTesting {