Bug 1613985 - Use default for equivalent-to-default constructors/dest…

…ructors in dom/broadcastchannel. r=smaug

Differential Revision: https://phabricator.services.mozilla.com/D63138

--HG--
extra : moz-landing-system : lando

dom/broadcastchannel/BroadcastChannel.cpp

@@ -129,7 +129,7 @@ class CloseRunnable final : public nsIRunnable, public nsICancelableRunnable {
   nsresult Cancel() override { return NS_OK; }
 
  private:
-  ~CloseRunnable() {}
+  ~CloseRunnable() = default;
 
   RefPtr<BroadcastChannel> mBC;
 };