[ash-md] Adds UMA depth count for Overview mode

ash/common/wm/overview/window_selector.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.

[tdanderson, 2016/06/24 00:17:50]

Please include a CL description (and cite the histogram name in the
description).

[varkha, 2016/06/24 16:31:39]

Done.

 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/common/wm/overview/window_selector.h"
 
 #include <algorithm>
 #include <functional>
 #include <set>
 #include <utility>
 #include <vector>
@@ skipping 436 matching lines @@
     // If the grid which became empty was the one with the selected window, we
     // need to select a window on the newly selected grid.
     if (selected_grid_index_ == index - 1)
       Move(LEFT, true);
   }
   if (grid_list_.empty())
     CancelSelection();
 }
 
 void WindowSelector::SelectWindow(WmWindow* window) {
   // Record UMA_WINDOW_OVERVIEW_ACTIVE_WINDOW_CHANGED if the user is selecting

[tdanderson, 2016/06/24 00:17:50]

Move this comment above line 464 or 465.

[varkha, 2016/06/24 16:31:39]

Done.

   // a window other than the window that was active prior to entering overview
   // mode (i.e., the window at the front of the MRU list).
   std::vector<WmWindow*> window_list =
       WmShell::Get()->GetMruWindowTracker()->BuildMruWindowList();
-  if (!window_list.empty() && window_list[0] != window) {
-    WmShell::Get()->RecordUserMetricsAction(
-        UMA_WINDOW_OVERVIEW_ACTIVE_WINDOW_CHANGED);
+  if (!window_list.empty()) {
+    if (window_list[0] != window) {
+      WmShell::Get()->RecordUserMetricsAction(
+          UMA_WINDOW_OVERVIEW_ACTIVE_WINDOW_CHANGED);
+    }
+    const auto it = std::find(window_list.begin(), window_list.end(), window);
+    if (it != window_list.end()) {
+      UMA_HISTOGRAM_COUNTS_100("Ash.WindowSelector.SelectionDepth",
+                               it - window_list.begin());
+    }
   }
 
   window->GetWindowState()->Activate();
 }
 
 bool WindowSelector::HandleKeyEvent(views::Textfield* sender,
                                     const ui::KeyEvent& key_event) {
   if (key_event.type() != ui::ET_KEY_PRESSED)
     return false;
 
@@ skipping 203 matching lines @@
   for (size_t i = 0; i <= grid_list_.size() &&
                      grid_list_[selected_grid_index_]->Move(direction, animate);
        i++) {
     selected_grid_index_ =
         (selected_grid_index_ + display_direction + grid_list_.size()) %
         grid_list_.size();
   }
 }
 
 }  // namespace ash