Added UMA stats to overview mode

ash/wm/overview/window_selector.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef ASH_WM_OVERVIEW_WINDOW_SELECTOR_H_
 #define ASH_WM_OVERVIEW_WINDOW_SELECTOR_H_
 
 #include <set>
 #include <vector>
 
@@ skipping 106 matching lines @@
   // this window.
   aura::Window* restore_focus_window_;
 
   // True when performing operations that may cause window activations. This is
   // used to prevent handling the resulting expected activation.
   bool ignore_activations_;
 
   // List of all the window overview grids, one for each root window.
   ScopedVector<WindowGrid> grid_list_;
 
-  // The time when overview was started.
-  base::Time overview_start_time_;
-
   // Tracks windows which were hidden because they were not part of the
   // overview.
   aura::WindowTracker hidden_windows_;
 
   // Tracks the index of the root window the selection widget is in.
   size_t selected_grid_index_;
 
+  // The following variables are used for metric collection purposes. All of
+  // them refer to this particular overview session and are not cumulative:
+  // The time when overview was started.
+  base::Time overview_start_time_;
+
+  // The number of arrow key presses.
+  size_t num_key_presses_;
+
+  // The number of items in the overview.
+  size_t num_items_;
+
   DISALLOW_COPY_AND_ASSIGN(WindowSelector);
 };
 
 }  // namespace ash
 
 #endif  // ASH_WM_OVERVIEW_WINDOW_SELECTOR_H_