Bug 1293603 (part 2) - Make Run() declarations consistent. r=erahm.

This patch makes most Run() declarations in subclasses of nsIRunnable have the
same form: |NS_IMETHOD Run() override|.

As a result of these changes, I had to add |override| to a couple of other
functions to satisfy clang's -Winconsistent-missing-override warning.

netwerk/protocol/websocket/WebSocketChannel.cpp

@@ -705,7 +705,7 @@ public:
       mListenerMT(mChannel->mListenerMT),
       mSize(aSize) {}
 
-  NS_IMETHOD Run()
+  NS_IMETHOD Run() override
   {
     MOZ_ASSERT(mChannel->IsOnTargetThread());
 
@@ -2282,7 +2282,7 @@ public:
     : mChannel(aChannel)
   {}
 
-  NS_IMETHOD Run()
+  NS_IMETHOD Run() override
   {
     nsCOMPtr<nsIObserverService> observerService =
       mozilla::services::GetObserverService();