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

ash/common/wm/overview/window_selector.cc

Index: ash/common/wm/overview/window_selector.cc
diff --git a/ash/common/wm/overview/window_selector.cc b/ash/common/wm/overview/window_selector.cc
index 3d79eb23d4d7415c005a8ef290b9bf74ad7f4acd..28665fe26077b073c119ea3eccc9e6d3b40d6b57 100644
--- a/ash/common/wm/overview/window_selector.cc
+++ b/ash/common/wm/overview/window_selector.cc
@@ -460,9 +460,16 @@ void WindowSelector::SelectWindow(WmWindow* window) {
   // 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();