Standardize usage of virtual/override/final specifiers.

ash/system/audio/volume_view.cc

Index: ash/system/audio/volume_view.cc
diff --git a/ash/system/audio/volume_view.cc b/ash/system/audio/volume_view.cc
index 821fb11533dabfa19c80b9ff5a546c1ae7aaa39f..b046b3586c437df2dabfcdfeba4ac5cdfcd82204 100644
--- a/ash/system/audio/volume_view.cc
+++ b/ash/system/audio/volume_view.cc
@@ -50,7 +50,7 @@ class VolumeButton : public views::ToggleImageButton {
     Update();
   }
 
-  virtual ~VolumeButton() {}
+  ~VolumeButton() override {}
 
   void Update() {
     float level =
@@ -72,7 +72,7 @@ class VolumeButton : public views::ToggleImageButton {
 
  private:
   // Overridden from views::View.
-  virtual gfx::Size GetPreferredSize() const override {
+  gfx::Size GetPreferredSize() const override {
     gfx::Size size = views::ToggleImageButton::GetPreferredSize();
     size.set_height(kTrayPopupItemHeight);
     return size;
@@ -99,7 +99,7 @@ class VolumeSlider : public views::Slider {
                 IDS_ASH_STATUS_TRAY_VOLUME));
     Update();
   }
-  virtual ~VolumeSlider() {}
+  ~VolumeSlider() override {}
 
   void Update() {
     UpdateState(!audio_delegate_->IsOutputAudioMuted());
@@ -115,15 +115,15 @@ class VolumeSlider : public views::Slider {
 class BarSeparator : public views::View {
  public:
   BarSeparator() {}
-  virtual ~BarSeparator() {}
+  ~BarSeparator() override {}
 
   // Overriden from views::View.
-  virtual gfx::Size GetPreferredSize() const override {
+  gfx::Size GetPreferredSize() const override {
     return gfx::Size(kBarSeparatorWidth, kBarSeparatorHeight);
   }
 
  private:
-  virtual void OnPaint(gfx::Canvas* canvas) override {
+  void OnPaint(gfx::Canvas* canvas) override {
     canvas->FillRect(gfx::Rect(width() / 2, 0, 1, height()),
                      kButtonStrokeColor);
   }