Bug 754457. Disallow copy-construction of ErrorResult, so it can only be passed by reference, not by value. r=peterv

dom/bindings/ErrorResult.h

@@ -47,6 +47,10 @@ public:
 
 private:
   nsresult mResult;
+
+  // Not to be implemented, to make sure people always pass this by
+  // reference, not by value.
+  ErrorResult(const ErrorResult&) MOZ_DELETE;
 };
 
 } // namespace mozilla