Standardize usage of virtual/override/final in mojo/

mojo/services/gles2/mojo_buffer_backing.h

Index: mojo/services/gles2/mojo_buffer_backing.h
diff --git a/mojo/services/gles2/mojo_buffer_backing.h b/mojo/services/gles2/mojo_buffer_backing.h
index 9304df7a7d0a61410267d43e22dae1b28cdbc9b8..079e98e568bf2fbbba5683db7f5e35b25513a5ad 100644
--- a/mojo/services/gles2/mojo_buffer_backing.h
+++ b/mojo/services/gles2/mojo_buffer_backing.h
@@ -18,14 +18,14 @@ class MojoBufferBacking : public gpu::BufferBacking {
   MojoBufferBacking(mojo::ScopedSharedBufferHandle handle,
                     void* memory,
                     size_t size);
-  virtual ~MojoBufferBacking();
+  ~MojoBufferBacking() override;
 
   static scoped_ptr<gpu::BufferBacking> Create(
       mojo::ScopedSharedBufferHandle handle,
       size_t size);
 
-  virtual void* GetMemory() const override;
-  virtual size_t GetSize() const override;
+  void* GetMemory() const override;
+  size_t GetSize() const override;
 
  private:
   mojo::ScopedSharedBufferHandle handle_;