Remove unused references to NativeTheme in TrayPopupItemStyle.

ash/common/system/tray/tray_details_view.h

Index: ash/common/system/tray/tray_details_view.h
diff --git a/ash/common/system/tray/tray_details_view.h b/ash/common/system/tray/tray_details_view.h
index 3fbf24d634a32d944af518bab7e56ab4060c0c47..4668d46824950468e22a16f45cea440b8858bf78 100644
--- a/ash/common/system/tray/tray_details_view.h
+++ b/ash/common/system/tray/tray_details_view.h
@@ -22,7 +22,6 @@ class OneShotTimer;
 namespace views {
 class BoxLayout;
 class CustomButton;
-class Label;
 class ProgressBar;
 }  // namespace views
 
@@ -96,13 +95,6 @@ class ASH_EXPORT TrayDetailsView : public views::View,
  private:
   friend class test::TrayDetailsViewTest;
 
-  // views::View:
-  void OnNativeThemeChanged(const ui::NativeTheme* theme) override;
-
-  // Updates the style of |label_| based on the current native theme, if it
-  // exists. Only used for material design.
-  void UpdateStyle();
-
   // Overridden to handle clicks on subclass-specific views.
   virtual void HandleViewClicked(views::View* view);
 
@@ -141,9 +133,6 @@ class ASH_EXPORT TrayDetailsView : public views::View,
   // The container view for the top-most title row in material design.
   TriView* tri_view_;
 
-  // The label used in the top-most title row for material design.
-  views::Label* label_;
-
   // The back button that appears in the material design title row. Not owned.
   views::Button* back_button_;