Add user action for changing the active window in Ash overview mode

ash/metrics/user_metrics_recorder.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_METRICS_USER_METRICS_RECORDER_H_
 #define ASH_METRICS_USER_METRICS_RECORDER_H_
 
 #include "ash/ash_export.h"
 #include "base/timer/timer.h"
 
@@ skipping 102 matching lines @@
   UMA_WINDOW_MAXIMIZE_BUTTON_CLICK_EXIT_FULLSCREEN,
   UMA_WINDOW_MAXIMIZE_BUTTON_CLICK_MAXIMIZE,
   UMA_WINDOW_MAXIMIZE_BUTTON_CLICK_MINIMIZE,
   UMA_WINDOW_MAXIMIZE_BUTTON_CLICK_RESTORE,
   UMA_WINDOW_MAXIMIZE_BUTTON_MAXIMIZE_LEFT,
   UMA_WINDOW_MAXIMIZE_BUTTON_MAXIMIZE_RIGHT,
 
   // Thumbnail sized overview of windows triggered by pressing the overview key.
   UMA_WINDOW_OVERVIEW,
 
+  // User selected a window in overview mode different from the
+  // previously-active window.
+  UMA_WINDOW_OVERVIEW_ACTIVE_WINDOW_CHANGED,
+
   // Selecting a window in overview mode by pressing the enter key.
   UMA_WINDOW_OVERVIEW_ENTER_KEY,
 
   // Window selection started by beginning an alt+tab cycle. This does not count
   // each step through an alt+tab cycle.
   UMA_WINDOW_CYCLE,
 };
 
 // User Metrics Recorder provides a repeating callback (RecordPeriodicMetrics)
 // on a timer to allow recording of state data over time to the UMA records.
@@ skipping 34 matching lines @@
 
   // The periodic timer that triggers metrics to be recorded.
   base::RepeatingTimer<UserMetricsRecorder> timer_;
 
   DISALLOW_COPY_AND_ASSIGN(UserMetricsRecorder);
 };
 
 }  // namespace ash
 
 #endif  // ASH_METRICS_USER_METRICS_RECORDER_H_