UMA data collection for docked windows

ash/wm/dock/docked_window_resizer.h

Index: ash/wm/dock/docked_window_resizer.h
diff --git a/ash/wm/dock/docked_window_resizer.h b/ash/wm/dock/docked_window_resizer.h
index 567b438a59024e1f86745c8c2c5225d18868bb45..fa708034c4fcc16ede5c5f8c44b285f724f3512d 100644
--- a/ash/wm/dock/docked_window_resizer.h
+++ b/ash/wm/dock/docked_window_resizer.h
@@ -10,6 +10,7 @@
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
+#include "base/time/time.h"
 
 namespace gfx {
 class Point;
@@ -70,6 +71,8 @@ class ASH_EXPORT DockedWindowResizer : public WindowResizer {
 
   gfx::Point last_location_;
 
+  base::Time last_docked_action_;
+
   // Wraps a window resizer and adds detaching / reattaching during drags.
   scoped_ptr<WindowResizer> next_window_resizer_;