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

components/view_manager/BUILD.gn

Index: components/view_manager/BUILD.gn
diff --git a/components/view_manager/BUILD.gn b/components/view_manager/BUILD.gn
index 4b66b36b663519bca7ec4e5160c12e6a04ab1e98..6c2df69fa5348a7c4a996ba4b192eb3c6edde462 100644
--- a/components/view_manager/BUILD.gn
+++ b/components/view_manager/BUILD.gn
@@ -61,6 +61,10 @@ source_set("view_manager_lib") {
     "view_manager_app.h",
     "view_manager_service_impl.cc",
     "view_manager_service_impl.h",
+    "window_activation_pre_target_handler.cc",
+    "window_activation_pre_target_handler.h",
+    "window_activation_pre_target_handler_observer.cc",
+    "window_activation_pre_target_handler_observer.h",
     "window_manager_access_policy.cc",
     "window_manager_access_policy.h",
   ]