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

content/browser/web_contents/aura/gesture_nav_simple.cc

Index: content/browser/web_contents/aura/gesture_nav_simple.cc
diff --git a/content/browser/web_contents/aura/gesture_nav_simple.cc b/content/browser/web_contents/aura/gesture_nav_simple.cc
index 4e83fdca5ea6710d006be3c34ebb8158e953f575..46ff45adc4af8140d1a53aae5909934b5464a057 100644
--- a/content/browser/web_contents/aura/gesture_nav_simple.cc
+++ b/content/browser/web_contents/aura/gesture_nav_simple.cc
@@ -54,10 +54,10 @@ class DeleteAfterAnimation : public ui::ImplicitAnimationObserver {
  private:
   friend class base::DeleteHelper<DeleteAfterAnimation<T> >;
 
-  virtual ~DeleteAfterAnimation() {}
+  ~DeleteAfterAnimation() override {}
 
   // ui::ImplicitAnimationObserver:
-  virtual void OnImplicitAnimationsCompleted() override {
+  void OnImplicitAnimationsCompleted() override {
     // Deleting an observer when a ScopedLayerAnimationSettings is iterating
     // over them can cause a crash (which can happen during tests). So instead,
     // schedule this observer to be deleted soon.