Moves maintaining ShellObservers back to Shell

ash/high_contrast/high_contrast_controller.cc

Index: ash/high_contrast/high_contrast_controller.cc
diff --git a/ash/high_contrast/high_contrast_controller.cc b/ash/high_contrast/high_contrast_controller.cc
index 38c0ee7ef7e1abf3fe8ef7e7d071e3f834692615..0cb98a52e5c25ddc01a03b60a1c2d7840605bebd 100644
--- a/ash/high_contrast/high_contrast_controller.cc
+++ b/ash/high_contrast/high_contrast_controller.cc
@@ -4,7 +4,6 @@
 
 #include "ash/high_contrast/high_contrast_controller.h"
 
-#include "ash/common/wm_shell.h"
 #include "ash/common/wm_window.h"
 #include "ash/shell.h"
 #include "ui/aura/window_event_dispatcher.h"
@@ -13,11 +12,11 @@
 namespace ash {
 
 HighContrastController::HighContrastController() : enabled_(false) {
-  WmShell::Get()->AddShellObserver(this);
+  Shell::GetInstance()->AddShellObserver(this);
 }
 
 HighContrastController::~HighContrastController() {
-  WmShell::Get()->RemoveShellObserver(this);
+  Shell::GetInstance()->RemoveShellObserver(this);
 }
 
 void HighContrastController::SetEnabled(bool enabled) {