[Extensions] Apply WARN_UNUSED_RESULT and final keyword to ExtensionFunctions.

chrome/browser/extensions/chrome_extension_function.h

Index: chrome/browser/extensions/chrome_extension_function.h
diff --git a/chrome/browser/extensions/chrome_extension_function.h b/chrome/browser/extensions/chrome_extension_function.h
index 4051ba18921a543af9073273df4b9b9c2f05070a..63ffbd761ecf869a9e47588db9778f5e50187b45 100644
--- a/chrome/browser/extensions/chrome_extension_function.h
+++ b/chrome/browser/extensions/chrome_extension_function.h
@@ -87,7 +87,7 @@ class ChromeAsyncExtensionFunction : public ChromeUIThreadExtensionFunction {
   static bool ValidationFailure(ChromeAsyncExtensionFunction* function);
 
  private:
-  ResponseAction Run() override;
+  ResponseAction Run() final;

[Devlin, 2015/02/24 17:04:42]

Even though there's about a half dozen of these, I think a basic comment like
"subclasses should implement RunAsync() instead." would be worthwhile here, so
that no one comes along and thinks it was put in errantly/flippantly.

[not at google - send to devlin, 2015/02/25 16:00:30]

"Should implement" contradicts the comment on line 72, so I've written a more
encouraging comment. Also scattered a few more comments around the place.

 };
 
 // A chrome specific analog to SyncExtensionFunction. This has access to a
@@ -111,7 +111,7 @@ class ChromeSyncExtensionFunction : public ChromeUIThreadExtensionFunction {
   static bool ValidationFailure(ChromeSyncExtensionFunction* function);
 
  private:
-  ResponseAction Run() override;
+  ResponseAction Run() final;
 };
 
 #endif  // CHROME_BROWSER_EXTENSIONS_CHROME_EXTENSION_FUNCTION_H_