Fix virtual/override/final usage in Source/platform/.

Source/platform/TimerTest.cpp

 // 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 "config.h"
 #include "platform/Timer.h"
 
 #include "public/platform/Platform.h"
 #include "public/platform/WebScheduler.h"
 #include "public/platform/WebThread.h"
@@ skipping 643 matching lines @@
     EXPECT_FLOAT_EQ(18.0, timer.nextFireInterval());
 
     runUntilIdleOrDeadlinePassed(m_startTime + 50.0);
     EXPECT_THAT(m_runTimes, ElementsAre(m_startTime + 20.0, m_startTime + 40.0));
 }
 
 class MockTimerWithAlignment : public TimerBase {
 public:
     MockTimerWithAlignment() : m_lastFireTime(0.0), m_alignedFireTime(0.0) { }
 
-    virtual void fired() override
+    void fired() override
     {
     }
 
     double alignedFireTime(double fireTime) const override
     {
         m_lastFireTime = fireTime;
         return m_alignedFireTime;
     }
 
     void setAlignedFireTime(double alignedFireTime)
@@ skipping 52 matching lines @@
     timer.didChangeAlignmentInterval(monotonicallyIncreasingTime());
 
     EXPECT_FLOAT_EQ(0.0, timer.nextFireInterval());
     EXPECT_FLOAT_EQ(0.0, timer.nextUnalignedFireInterval());
     EXPECT_FLOAT_EQ(m_startTime, timer.lastFireTime());
 }
 
 
 } // namespace
 } // namespace blink