Replace OVERRIDE with their C++11 counterparts in extensions

This is fix for newly added OVERRIDE construts in extensions folder.
This step is a giant search and replace for OVERRIDE and FINAL to
replace them with their lowercase versions.

BUG=417463

Review URL: https://codereview.chromium.org/658453002

Cr-Commit-Position: refs/heads/master@{#299448}

extensions/browser/guest_view/web_view/web_view_apitest.cc

@@ -82,7 +82,7 @@ class WebContentsHiddenObserver : public content::WebContentsObserver {
   }
 
   // WebContentsObserver.
-  virtual void WasHidden() OVERRIDE {
+  virtual void WasHidden() override {
     hidden_observed_ = true;
     hidden_callback_.Run();
   }