Update {virtual,override,final} to follow C++11 style.

chrome/browser/android/thumbnail/thumbnail_store.h

Index: chrome/browser/android/thumbnail/thumbnail_store.h
diff --git a/chrome/browser/android/thumbnail/thumbnail_store.h b/chrome/browser/android/thumbnail/thumbnail_store.h
index 94cdbba27cb9a80e17c4cec5200ac49e6efed4fc..8ad0c1a14f991d9ed64ea833f41538d5a030f20c 100644
--- a/chrome/browser/android/thumbnail/thumbnail_store.h
+++ b/chrome/browser/android/thumbnail/thumbnail_store.h
@@ -50,7 +50,7 @@ class ThumbnailStore : ThumbnailDelegate {
                  size_t write_queue_max_size,
                  bool use_approximation_thumbnail);
 
-  virtual ~ThumbnailStore();
+  ~ThumbnailStore() override;
 
   void SetUIResourceProvider(ui::UIResourceProvider* ui_resource_provider);
 
@@ -72,7 +72,7 @@ class ThumbnailStore : ThumbnailDelegate {
           post_decompress_callback);
 
   // ThumbnailDelegate implementation
-  virtual void InvalidateCachedThumbnail(Thumbnail* thumbnail) override;
+  void InvalidateCachedThumbnail(Thumbnail* thumbnail) override;
 
  private:
   class ThumbnailMetaData {