Bug 777734 - Initialize the type variable in ParamTraits<nsMouseEvent>::Read; r=cjones

This is mostly to silence compiler warnings. The uninitialized type itself
won't cause problems because failed Read() prevents dispatch.

--HG--
extra : rebase_source : 094cb8c69357487bf321c6d558a8511656eaec58

widget/nsGUIEventIPC.h

@@ -136,7 +136,7 @@ struct ParamTraits<nsMouseEvent>
   static bool Read(const Message* aMsg, void** aIter, paramType* aResult)
   {
     bool rv;
-    PRUint8 reason, context, exit;
+    PRUint8 reason = 0, context = 0, exit = 0;
     rv = ReadParam(aMsg, aIter, static_cast<nsMouseEvent_base*>(aResult)) &&
          ReadParam(aMsg, aIter, &aResult->ignoreRootScrollFrame) &&
          ReadParam(aMsg, aIter, &reason) &&