exo: Clean up cursor code

components/exo/wm_helper_ash.cc

Index: components/exo/wm_helper_ash.cc
diff --git a/components/exo/wm_helper_ash.cc b/components/exo/wm_helper_ash.cc
index 1a025097a110f50d620638f4a11c7b3d6d3860a9..453b547c04004730be765dfbccbdd5d27eabcd9e 100644
--- a/components/exo/wm_helper_ash.cc
+++ b/components/exo/wm_helper_ash.cc
@@ -22,6 +22,7 @@ namespace exo {
 WMHelperAsh::WMHelperAsh() {
   ash::Shell::GetInstance()->AddShellObserver(this);
   ash::Shell::GetInstance()->activation_client()->AddObserver(this);
+  ash::Shell::GetInstance()->cursor_manager()->AddObserver(this);
   ash::Shell::GetInstance()->window_tree_host_manager()->AddObserver(this);
   aura::client::FocusClient* focus_client =
       aura::client::GetFocusClient(ash::Shell::GetPrimaryRootWindow());
@@ -37,6 +38,7 @@ WMHelperAsh::~WMHelperAsh() {
       aura::client::GetFocusClient(ash::Shell::GetPrimaryRootWindow());
   focus_client->RemoveObserver(this);
   ash::Shell::GetInstance()->window_tree_host_manager()->RemoveObserver(this);
+  ash::Shell::GetInstance()->cursor_manager()->RemoveObserver(this);
   ash::Shell::GetInstance()->activation_client()->RemoveObserver(this);
   ash::Shell::GetInstance()->RemoveShellObserver(this);
   ui::DeviceDataManager::GetInstance()->RemoveObserver(this);