Add the "virtual" keyword on method overrides that are missing it.

app/slide_animation.h

Index: app/slide_animation.h
diff --git a/app/slide_animation.h b/app/slide_animation.h
index 91e64bc79e3b3370ce5311f395c61c5fab01f326..d073db16adc9e5ac2a8a9314380b3e9a88ddeb93 100644
--- a/app/slide_animation.h
+++ b/app/slide_animation.h
@@ -65,13 +65,13 @@ class SlideAnimation : public LinearAnimation {
   int GetSlideDuration() const { return slide_duration_; }
   void SetTweenType(Tween::Type tween_type) { tween_type_ = tween_type; }
 
-  double GetCurrentValue() const { return value_current_; }
+  virtual double GetCurrentValue() const { return value_current_; }
   bool IsShowing() const { return showing_; }
   bool IsClosing() const { return !showing_ && value_end_ < value_current_; }
 
  private:
   // Overridden from Animation.
-  void AnimateToState(double state);
+  virtual void AnimateToState(double state);
 
   AnimationDelegate* target_;