Bug 778070: Trigger ProtocolErrorBreakpoint() on message-handler |return false/null;|. r=bent

ipc/ipdl/ipdl/lower.py

@@ -4929,7 +4929,10 @@ class _GenerateProtocolActorCode(ipdl.ast.Visitor):
                      args=md.makeCxxArgs(params=1,
                                          retsems='in', retcallsems='out',
                                          implicit=implicit))))
-        failif.addifstmt(StmtReturn(_Result.ProcessingError))
+        failif.addifstmts([
+            _protocolErrorBreakpoint('Handler for '+ md.name +' returned error code'),
+            StmtReturn(_Result.ProcessingError) 
+        ])
         return [ failif ]
 
     def makeDtorMethodDecl(self, md):