Add UMA for first app list paint on Windows.

chrome/browser/ui/app_list/app_list_service.h

Index: chrome/browser/ui/app_list/app_list_service.h
diff --git a/chrome/browser/ui/app_list/app_list_service.h b/chrome/browser/ui/app_list/app_list_service.h
index 441fdc1ea7b7e143fc37ee53ec5c56cf7efcac19..60144f08f910406ef9ff44ae41ddb303dae37068 100644
--- a/chrome/browser/ui/app_list/app_list_service.h
+++ b/chrome/browser/ui/app_list/app_list_service.h
@@ -8,6 +8,7 @@
 #include <string>
 
 #include "base/basictypes.h"
+#include "base/callback_forward.h"
 #include "base/compiler_specific.h"
 #include "ui/gfx/native_widget_types.h"
 
@@ -36,6 +37,10 @@ class AppListService {
 
   static void RecordShowTimings(const CommandLine& command_line);
 
+  // Indicates that |callback| should be called next time the app list is
+  // painted.
+  virtual void SetAppListNextPaintCallback(const base::Closure& callback) = 0;
+
   // Perform Chrome first run logic. This is executed before Chrome's threads
   // have been created.
   virtual void HandleFirstRun() = 0;