Add test for power_menu_button.

chrome/browser/chromeos/status/power_menu_button.h

Index: chrome/browser/chromeos/status/power_menu_button.h
===================================================================
--- chrome/browser/chromeos/status/power_menu_button.h	(revision 42551)
+++ chrome/browser/chromeos/status/power_menu_button.h	(working copy)
@@ -46,6 +46,8 @@
   // PowerLibrary::Observer implementation.
   virtual void PowerChanged(PowerLibrary* obj);
 
+  const int icon_id() const { return icon_id_; }
+
  protected:
   // StatusAreaButton implementation.
   virtual void DrawPressed(gfx::Canvas* canvas);
@@ -67,6 +69,9 @@
   // The power menu.
   views::Menu2 power_menu_;
 
+  // The currently showing icon bitmap id.
+  int icon_id_;
+
   DISALLOW_COPY_AND_ASSIGN(PowerMenuButton);
 };