Make UserActivityDetector a singleton

extensions/shell/browser/shell_browser_main_parts.cc

Index: extensions/shell/browser/shell_browser_main_parts.cc
diff --git a/extensions/shell/browser/shell_browser_main_parts.cc b/extensions/shell/browser/shell_browser_main_parts.cc
index e9708f1772d401fb09e7a5ee80850a33eee8ebd1..c1ffd090339a0d86e93699230bb2f6b8203f4d1a 100644
--- a/extensions/shell/browser/shell_browser_main_parts.cc
+++ b/extensions/shell/browser/shell_browser_main_parts.cc
@@ -33,6 +33,7 @@
 #include "ui/aura/window_tree_host.h"
 #include "ui/base/ime/input_method_initializer.h"
 #include "ui/base/resource/resource_bundle.h"
+#include "ui/wm/core/user_activity_detector.h"
 
 #if !defined(OS_ANDROID) && !defined(OS_IOS)
 #include "components/storage_monitor/storage_monitor.h"
@@ -124,6 +125,9 @@ void ShellBrowserMainParts::PreMainMessageLoopRun() {
   storage_monitor::StorageMonitor::Create();
 #endif
 
+  // UserActivityDetector must be created prior to |desktop_controller_|.
+  wm::UserActivityDetector::Create();
+
   desktop_controller_.reset(browser_main_delegate_->CreateDesktopController());
 
   // NOTE: Much of this is culled from chrome/test/base/chrome_test_suite.cc
@@ -215,6 +219,8 @@ void ShellBrowserMainParts::PostMainMessageLoopRun() {
 
   desktop_controller_.reset();
 
+  wm::UserActivityDetector::Shutdown();
+
 #if !defined(OS_ANDROID) && !defined(OS_IOS)
   storage_monitor::StorageMonitor::Destroy();
 #endif