Standardize usage of virtual/override/final in base/

base/memory/discardable_memory_emulated.h

Index: base/memory/discardable_memory_emulated.h
diff --git a/base/memory/discardable_memory_emulated.h b/base/memory/discardable_memory_emulated.h
index 33889ad9a6d4686e5f91572425bfab763ab9eb15..0dc15e393558b99f7c4e8a088197b0bba6757a10 100644
--- a/base/memory/discardable_memory_emulated.h
+++ b/base/memory/discardable_memory_emulated.h
@@ -17,7 +17,7 @@ class DiscardableMemoryEmulated
       public internal::DiscardableMemoryManagerAllocation {
  public:
   explicit DiscardableMemoryEmulated(size_t bytes);
-  virtual ~DiscardableMemoryEmulated();
+  ~DiscardableMemoryEmulated() override;
 
   static bool ReduceMemoryUsage();
 
@@ -31,14 +31,14 @@ class DiscardableMemoryEmulated
   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:
   const size_t bytes_;