Add VectorIconButton functionality to ImageButton.

ash/common/system/date/date_default_view.h

Index: ash/common/system/date/date_default_view.h
diff --git a/ash/common/system/date/date_default_view.h b/ash/common/system/date/date_default_view.h
index 6adaee0b61513f7dfc5cf69ed4ad6862fd289ee1..17362624d0cddfc5129fcf108d6b5817479b185f 100644
--- a/ash/common/system/date/date_default_view.h
+++ b/ash/common/system/date/date_default_view.h
@@ -8,7 +8,7 @@
 #include "ash/ash_export.h"
 #include "ash/common/login_status.h"
 #include "base/macros.h"
-#include "ui/views/controls/button/button.h"
+#include "ui/views/controls/button/image_button.h"
 #include "ui/views/view.h"
 
 namespace ash {
@@ -24,7 +24,7 @@ class TrayPopupHeaderButton;
 // TODO(tdanderson): Remove this class once material design is enabled by
 // default. See crbug.com/614453.
 class ASH_EXPORT DateDefaultView : public views::View,
-                                   public views::ButtonListener {
+                                   public views::ImageButtonDelegate {
  public:
   DateDefaultView(SystemTrayItem* owner, LoginStatus login);
 
@@ -37,7 +37,7 @@ class ASH_EXPORT DateDefaultView : public views::View,
   const tray::DateView* GetDateView() const;
 
  private:
-  // Overridden from views::ButtonListener.
+  // views::ImageButtonDelegate:
   void ButtonPressed(views::Button* sender, const ui::Event& event) override;
 
   TrayPopupHeaderButton* help_button_;