Mojo C++ Bindings: Add helpers for bad message reporting

mojo/edk/system/core.cc

Index: mojo/edk/system/core.cc
diff --git a/mojo/edk/system/core.cc b/mojo/edk/system/core.cc
index b2abf0f2951e389d928d82295617dea5ee7857ce..4bb07eaf3886bb113df9dbbd3bbb4c0c681751b5 100644
--- a/mojo/edk/system/core.cc
+++ b/mojo/edk/system/core.cc
@@ -167,6 +167,11 @@ scoped_refptr<Dispatcher> Core::GetDispatcher(MojoHandle handle) {
   return handles_.GetDispatcher(handle);
 }
 
+void Core::SetDefaultProcessErrorCallback(
+    const ProcessErrorCallback& callback) {
+  default_process_error_callback_ = callback;
+}
+
 void Core::AddChild(base::ProcessHandle process_handle,
                     ScopedPlatformHandle platform_handle,
                     const std::string& child_token,
@@ -772,6 +777,8 @@ MojoResult Core::NotifyBadMessage(MojoMessageHandle message,
       reinterpret_cast<MessageForTransit*>(message)->ports_message();
   if (ports_message.source_node() == ports::kInvalidNodeName) {
     DVLOG(1) << "Received invalid message from unknown node.";
+    if (!default_process_error_callback_.is_null())
+      default_process_error_callback_.Run(std::string(error, error_num_bytes));
     return MOJO_RESULT_OK;
   }