cros: Fix various small issues with cast tray entry.

ash/common/system/chromeos/screen_security/screen_tray_item.h

Index: ash/common/system/chromeos/screen_security/screen_tray_item.h
diff --git a/ash/common/system/chromeos/screen_security/screen_tray_item.h b/ash/common/system/chromeos/screen_security/screen_tray_item.h
index a0e94b4f86a1b4e8688b6e0aee5ce1065e254fac..67a531eb33cb99ce6c5237410d794a4df80ae56d 100644
--- a/ash/common/system/chromeos/screen_security/screen_tray_item.h
+++ b/ash/common/system/chromeos/screen_security/screen_tray_item.h
@@ -55,6 +55,7 @@ class ScreenStatusView : public views::View, public views::ButtonListener {
  protected:
   views::ImageView* icon() { return icon_; }
   views::Label* label() { return label_; }
+  views::Button* stop_button() { return stop_button_; }
 
   // Overridden from views::View:
   void OnNativeThemeChanged(const ui::NativeTheme* theme) override;
@@ -64,7 +65,7 @@ class ScreenStatusView : public views::View, public views::ButtonListener {
   ScreenTrayItem* screen_tray_item_;
   views::ImageView* icon_;
   views::Label* label_;
-  views::View* stop_button_;
+  views::Button* stop_button_;
   base::string16 label_text_;
   base::string16 stop_button_text_;