Moves maintaining ShellObservers back to Shell

ash/wm/video_detector.cc

Index: ash/wm/video_detector.cc
diff --git a/ash/wm/video_detector.cc b/ash/wm/video_detector.cc
index 18d9704e9da432f898bc8c2e6c4c51168995ab98..6a7779c116a8c09a14580f352f888b8377c3ab8b 100644
--- a/ash/wm/video_detector.cc
+++ b/ash/wm/video_detector.cc
@@ -84,11 +84,11 @@ VideoDetector::VideoDetector()
       window_observer_manager_(this),
       is_shutting_down_(false) {
   aura::Env::GetInstance()->AddObserver(this);
-  WmShell::Get()->AddShellObserver(this);
+  Shell::GetInstance()->AddShellObserver(this);
 }
 
 VideoDetector::~VideoDetector() {
-  WmShell::Get()->RemoveShellObserver(this);
+  Shell::GetInstance()->RemoveShellObserver(this);
   aura::Env::GetInstance()->RemoveObserver(this);
 }