Add a test of updating cached height for popup notifications

ash/system/web_notification/ash_popup_alignment_delegate.h

Index: ash/system/web_notification/ash_popup_alignment_delegate.h
diff --git a/ash/system/web_notification/ash_popup_alignment_delegate.h b/ash/system/web_notification/ash_popup_alignment_delegate.h
index 50b70621a5748d17eea727bdbdb7b0e911017fec..b81f277087fa058a3944df8d23a97aaa3fa56655 100644
--- a/ash/system/web_notification/ash_popup_alignment_delegate.h
+++ b/ash/system/web_notification/ash_popup_alignment_delegate.h
@@ -48,6 +48,9 @@ class ASH_EXPORT AshPopupAlignmentDelegate
   // can avoid it.
   void SetSystemTrayHeight(int height);
 
+  // Returns the current system tray height.

[Mr4D (OOO till 08-26), 2016/05/27 14:01:06]

Since this is only used by tests - could you please rename this to
system_tray_height_for_test() and maybe mention that it is only used for a test?

[yoshiki, 2016/05/30 03:54:54]

Done.

+  int system_tray_height() const { return system_tray_height_; }
+
   // Overridden from message_center::PopupAlignmentDelegate:
   int GetToastOriginX(const gfx::Rect& toast_bounds) const override;
   int GetBaseLine() const override;