Add UMA for first app list paint on Windows.

ui/app_list/views/app_list_view.h

Index: ui/app_list/views/app_list_view.h
diff --git a/ui/app_list/views/app_list_view.h b/ui/app_list/views/app_list_view.h
index fff4815ba1bcbedc46b8c6156ea4dd2c4ffd7acb..b1b2554a6bf0a04c14c36325d2e990c3742906a9 100644
--- a/ui/app_list/views/app_list_view.h
+++ b/ui/app_list/views/app_list_view.h
@@ -5,6 +5,7 @@
 #ifndef UI_APP_LIST_VIEWS_APP_LIST_VIEW_H_
 #define UI_APP_LIST_VIEWS_APP_LIST_VIEW_H_
 
+#include "base/callback_forward.h"
 #include "base/memory/scoped_ptr.h"
 #include "ui/app_list/app_list_export.h"
 #include "ui/app_list/signin_delegate_observer.h"
@@ -61,6 +62,7 @@ class APP_LIST_EXPORT AppListView : public views::BubbleDelegateView,
 
   // Overridden from views::View:
   virtual gfx::Size GetPreferredSize() OVERRIDE;
+  virtual void Paint(gfx::Canvas* canvas) OVERRIDE;
 
   // WidgetDelegate overrides:
   virtual bool ShouldHandleSystemCommands() const OVERRIDE;
@@ -70,6 +72,9 @@ class APP_LIST_EXPORT AppListView : public views::BubbleDelegateView,
   // Invoked when the sign-in status is changed to switch on/off sign-in view.
   void OnSigninStatusChanged();
 
+  // Set a callback to be called the next time any app list paints.
+  static void SetAppListNextPaintCallback(const base::Closure& callback);
+
 #if defined(OS_WIN)
   HWND GetHWND() const;
 #endif