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

ash/wm/overview/window_selector_controller.cc

Index: ash/wm/overview/window_selector_controller.cc
diff --git a/ash/wm/overview/window_selector_controller.cc b/ash/wm/overview/window_selector_controller.cc
index 73b9c148146c1129afb2de9ddd2c4f98de5ff4cc..a3810290c33040629d0d5e7c397961c6287eeef2 100644
--- a/ash/wm/overview/window_selector_controller.cc
+++ b/ash/wm/overview/window_selector_controller.cc
@@ -20,7 +20,8 @@
 
 namespace ash {
 
-WindowSelectorController::WindowSelectorController() {
+WindowSelectorController::WindowSelectorController()
+    : initially_active_window_(nullptr) {
 }
 
 WindowSelectorController::~WindowSelectorController() {
@@ -57,6 +58,7 @@ void WindowSelectorController::ToggleOverview() {
     if (windows.empty())
       return;
 
+    OnSelectionStarting();
     Shell::GetInstance()->OnOverviewModeStarting();
     window_selector_.reset(new WindowSelector(this));
     window_selector_->Init(windows);
@@ -80,6 +82,23 @@ void WindowSelectorController::OnSelectionEnded() {
   window_selector_.reset();
   last_selection_time_ = base::Time::Now();
   Shell::GetInstance()->OnOverviewModeEnded();
+
+  // Record UMA_WINDOW_OVERVIEW_ACTIVE_WINDOW_CHANGED if the active window
+  // is different from the window that was active upon entering overview
+  // mode.
+  aura::Window* active = wm::GetActiveWindow();

[bruthig, 2015/05/12 17:37:38]

I feel like this metric should only be recorded if the window change was
actually due to someone selecting a window from the WindowSelector UI.

I'm concerned that the |active| window here could be set by a different task
switching mechanism (ie alt+tab or clicking a docked window) and that this
metric will be double counted in the those two buckets.

[oshima, 2015/05/12 20:25:13]

This may also change if the window is closed or an app requested focus
explicitly. It's probably rare, and I don't have strong opinion here so let me
know when both of you agreed, and I'll review again.

[tdanderson, 2015/05/14 01:36:32]

In patch set 2 the user action won't be recorded when closing windows in
overview mode. It will still be recorded if a window requests focus
programmatically, but that is rare and Ben and I have agreed we can live with
having that small amount of noise in the data.

+  if (initially_active_window_ && active &&
+      active != initially_active_window_) {
+    Shell::GetInstance()->metrics()->RecordUserMetricsAction(
+        UMA_WINDOW_OVERVIEW_ACTIVE_WINDOW_CHANGED);
+  }
+  initially_active_window_ = nullptr;
+}
+
+void WindowSelectorController::OnSelectionStarting() {

[bruthig, 2015/05/12 17:37:38]

It would be less invasive to WindowSelectorController and would allow the future
work for the catch-all TaskChanged metric to be centralized if
OnSelectionStarting, OnSelectionStarted, OnSelectionEnding and OnSelectionEnded
were events that a WindowSelectorObserver.

It is worth considering but may be too risky this close to branch cut.

[tdanderson, 2015/05/14 01:36:32]

Not pursuing this as per in-person discussion.

+  aura::Window* active = wm::GetActiveWindow();
+  if (active && WindowSelector::IsSelectable(active))
+    initially_active_window_ = active;
 }
 
 void WindowSelectorController::OnSelectionStarted() {