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

mojo/edk/embedder/embedder.h

Index: mojo/edk/embedder/embedder.h
diff --git a/mojo/edk/embedder/embedder.h b/mojo/edk/embedder/embedder.h
index ffd513d6cd01dc159f9bcff6083bc7cd3a8e5768..e4a8420e8050aa25228aea7f99cfbb96b31aceb9 100644
--- a/mojo/edk/embedder/embedder.h
+++ b/mojo/edk/embedder/embedder.h
@@ -74,6 +74,11 @@ MOJO_SYSTEM_IMPL_EXPORT void SetParentPipeHandleFromCommandLine();
 // initialize the (global, singleton) system.
 MOJO_SYSTEM_IMPL_EXPORT void Init();
 
+// Sets a default callback to invoke when an internal error is reported but
+// cannot be associated with a specific child process.
+MOJO_SYSTEM_IMPL_EXPORT void SetDefaultProcessErrorCallback(
+    const ProcessErrorCallback& callback);
+
 // Basic functions -------------------------------------------------------------
 
 // The functions in this section are available once |Init()| has been called.