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.

toolkit/components/satchel/nsFormFillController.cpp

@@ -725,7 +725,7 @@ public:
     MOZ_ASSERT(mObserver, "You shouldn't call this runnable with a null observer!");
   }
 
-  NS_IMETHOD Run() {
+  NS_IMETHOD Run() override {
     mObserver->OnUpdateSearchResult(mSearch, mResult);
     return NS_OK;
   }