Added UMA statistics for changing the active window via click or touch events.

ui/views/widget/desktop_aura/desktop_native_widget_aura.cc

Index: ui/views/widget/desktop_aura/desktop_native_widget_aura.cc
diff --git a/ui/views/widget/desktop_aura/desktop_native_widget_aura.cc b/ui/views/widget/desktop_aura/desktop_native_widget_aura.cc
index c82ced73bb74b4175c43a6b5da51e8dc80031b95..d959ac0aa9b84ec3b59533c32a54d29436ce514e 100644
--- a/ui/views/widget/desktop_aura/desktop_native_widget_aura.cc
+++ b/ui/views/widget/desktop_aura/desktop_native_widget_aura.cc
@@ -56,6 +56,7 @@
 #include "ui/wm/core/shadow_controller.h"
 #include "ui/wm/core/shadow_types.h"
 #include "ui/wm/core/visibility_controller.h"
+#include "ui/wm/core/window_activation_pre_target_handler.h"
 #include "ui/wm/core/window_animations.h"
 #include "ui/wm/core/window_modality_controller.h"
 #include "ui/wm/public/activation_client.h"
@@ -320,7 +321,9 @@ void DesktopNativeWidgetAura::OnHostClosed() {
   // have to worry about the possibility of FocusController attempting to use
   // |content_window_| after it's been destroyed but before all child windows
   // have been destroyed.
-  host_->window()->RemovePreTargetHandler(focus_client_.get());
+  host_->window()->RemovePreTargetHandler(
+      window_activation_pretarget_handler_.get());
+  window_activation_pretarget_handler_.reset();
   aura::client::SetFocusClient(host_->window(), NULL);
   aura::client::SetActivationClient(host_->window(), NULL);
   focus_client_.reset();
@@ -478,7 +481,10 @@ void DesktopNativeWidgetAura::InitNativeWidget(
   focus_client_.reset(focus_controller);
   aura::client::SetFocusClient(host_->window(), focus_controller);
   aura::client::SetActivationClient(host_->window(), focus_controller);
-  host_->window()->AddPreTargetHandler(focus_controller);
+  window_activation_pretarget_handler_.reset(

[sky, 2015/05/27 15:37:52]

I don't like separating out activation from the focus controller. It means you
either have to duplicate checks done in the focuscontroller (bad) or skip them
(worse).

I'm still not clear on what you hope to gain from these metrics, but why not add
the information you need to ActivationChangeObserver::OnWindowActivated?

+      new ::wm::WindowActivationPreTargetHandler(focus_client_.get()));
+  host_->window()->AddPreTargetHandler(
+      window_activation_pretarget_handler_.get());
 
   dispatcher_client_.reset(new DesktopDispatcherClient);
   aura::client::SetDispatcherClient(host_->window(),