Enforce marking "override" for functions overriding Blink in components/.

components/scheduler/renderer/webthread_impl_for_renderer_scheduler_unittest.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/scheduler/renderer/webthread_impl_for_renderer_scheduler.h"
 
 #include "base/location.h"
 #include "base/run_loop.h"
 #include "base/single_thread_task_runner.h"
 #include "components/scheduler/child/scheduler_task_runner_delegate_impl.h"
@@ skipping 131 matching lines @@
   thread_.taskRunner()->postTask(blink::WebTraceLocation(), task2.release());
   thread_.taskRunner()->postTask(blink::WebTraceLocation(), task3.release());
   message_loop_.RunUntilIdle();
   thread_.removeTaskObserver(&observer);
 }
 
 class ExitRunLoopTask : public blink::WebTaskRunner::Task {
  public:
   ExitRunLoopTask(base::RunLoop* run_loop) : run_loop_(run_loop) {}
 
-  virtual void run() { run_loop_->Quit(); }
+  void run() override { run_loop_->Quit(); }
 
  private:
   base::RunLoop* run_loop_;
 };
 
 void EnterRunLoop(base::MessageLoop* message_loop, blink::WebThread* thread) {
   // Note: WebThreads do not support nested run loops, which is why we use a
   // run loop directly.
   base::RunLoop run_loop;
   thread->taskRunner()->postTask(blink::WebTraceLocation(),
@@ skipping 21 matching lines @@
   }
 
   message_loop_.task_runner()->PostTask(
       FROM_HERE, base::Bind(&EnterRunLoop, base::Unretained(&message_loop_),
                             base::Unretained(&thread_)));
   message_loop_.RunUntilIdle();
   thread_.removeTaskObserver(&observer);
 }
 
 }  // namespace scheduler