Standardize usage of virtual/override/final in base/

base/memory/discardable_memory_mach.h

 // Copyright 2014 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.
 
 #ifndef BASE_MEMORY_DISCARDABLE_MEMORY_MACH_H_
 #define BASE_MEMORY_DISCARDABLE_MEMORY_MACH_H_
 
 #include "base/memory/discardable_memory.h"
 
 #include "base/mac/scoped_mach_vm.h"
 #include "base/memory/discardable_memory_manager.h"
 
 namespace base {
 namespace internal {
 
 class DiscardableMemoryMach
     : public DiscardableMemory,
       public internal::DiscardableMemoryManagerAllocation {
  public:
   explicit DiscardableMemoryMach(size_t bytes);
-  virtual ~DiscardableMemoryMach();
+  ~DiscardableMemoryMach() override;
 
   static void PurgeForTesting();
 
   bool Initialize();
 
   // Overridden from DiscardableMemory:
-  virtual DiscardableMemoryLockStatus Lock() override;
-  virtual void Unlock() override;
-  virtual void* Memory() const override;
+  DiscardableMemoryLockStatus Lock() override;
+  void Unlock() override;
+  void* Memory() const override;
 
   // Overridden from internal::DiscardableMemoryManagerAllocation:
-  virtual bool AllocateAndAcquireLock() override;
-  virtual void ReleaseLock() override;
-  virtual void Purge() override;
+  bool AllocateAndAcquireLock() override;
+  void ReleaseLock() override;
+  void Purge() override;
 
  private:
   mac::ScopedMachVM memory_;
   const size_t bytes_;
   bool is_locked_;
 
   DISALLOW_COPY_AND_ASSIGN(DiscardableMemoryMach);
 };
 
 }  // namespace internal
 }  // namespace base
 
 #endif  // BASE_MEMORY_DISCARDABLE_MEMORY_MACH_H_