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

ui/wm/core/window_activation_pre_target_handler_observer.cc

Index: ui/wm/core/window_activation_pre_target_handler_observer.cc
diff --git a/ui/wm/core/window_activation_pre_target_handler_observer.cc b/ui/wm/core/window_activation_pre_target_handler_observer.cc
new file mode 100644
index 0000000000000000000000000000000000000000..6c45553e2d5e1a9bdaa1d645d745bc1bf33c45b2
--- /dev/null
+++ b/ui/wm/core/window_activation_pre_target_handler_observer.cc
@@ -0,0 +1,17 @@
+// Copyright 2015 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.
+
+#include "ui/wm/core/window_activation_pre_target_handler_observer.h"
+
+namespace wm {
+
+WindowActivationPreTargetHandlerObserver::
+    WindowActivationPreTargetHandlerObserver() {
+}
+
+WindowActivationPreTargetHandlerObserver::
+    ~WindowActivationPreTargetHandlerObserver() {
+}
+
+}  // namespace wm