Make UserActivityDetector a singleton

ui/wm/core/user_activity_detector.cc

Index: ui/wm/core/user_activity_detector.cc
diff --git a/ui/wm/core/user_activity_detector.cc b/ui/wm/core/user_activity_detector.cc
index 56bf563b3d032f11b34b87a5af295b78f11c4b7e..666cc3164080f9d42fc4701820535b7386d9d624 100644
--- a/ui/wm/core/user_activity_detector.cc
+++ b/ui/wm/core/user_activity_detector.cc
@@ -14,6 +14,8 @@ namespace wm {
 
 namespace {
 
+UserActivityDetector* g_instance = NULL;

[oshima, 2014/10/31 16:53:31]

My preference is no g_ for file scoped variable as it's for global scoepd
variable, but i'll leave this to owners.

+
 // Returns a string describing |event|.
 std::string GetEventDebugString(const ui::Event* event) {
   std::string details = base::StringPrintf(
@@ -43,10 +45,22 @@ const int UserActivityDetector::kNotifyIntervalMs = 200;
 // and we'll ignore legitimate activity.
 const int UserActivityDetector::kDisplayPowerChangeIgnoreMouseMs = 1000;
 
-UserActivityDetector::UserActivityDetector() {
+// static
+void UserActivityDetector::Create() {
+  CHECK(!g_instance);
+  g_instance = new UserActivityDetector();

[oshima, 2014/10/31 16:53:31]

Initialize in ctor/dtor.

 }
 
-UserActivityDetector::~UserActivityDetector() {
+// static
+void UserActivityDetector::Shutdown() {
+  CHECK(g_instance);
+  delete g_instance;
+  g_instance = NULL;
+}
+
+// static
+UserActivityDetector* UserActivityDetector::Get() {
+  return g_instance;
 }
 
 bool UserActivityDetector::HasObserver(UserActivityObserver* observer) const {
@@ -92,6 +106,12 @@ void UserActivityDetector::OnGestureEvent(ui::GestureEvent* event) {
   HandleActivity(event);
 }
 
+UserActivityDetector::UserActivityDetector() {
+}
+
+UserActivityDetector::~UserActivityDetector() {
+}
+
 base::TimeTicks UserActivityDetector::GetCurrentTime() const {
   return !now_for_test_.is_null() ? now_for_test_ : base::TimeTicks::Now();
 }