Remove ash::ScopedObserverWithDuplicatedSources

ash/shelf/shelf_window_watcher.cc

Index: ash/shelf/shelf_window_watcher.cc
diff --git a/ash/shelf/shelf_window_watcher.cc b/ash/shelf/shelf_window_watcher.cc
index 6ca0240b2685a16c6b4e0ac0767717cbb30da19a..e9e73e83e4962561fc084bd5c8ee605161b160cf 100644
--- a/ash/shelf/shelf_window_watcher.cc
+++ b/ash/shelf/shelf_window_watcher.cc
@@ -105,10 +105,8 @@ ShelfWindowWatcher::ShelfWindowWatcher(ShelfModel* model)
       removed_window_observer_(this),
       observed_windows_(this),
       observed_root_windows_(&root_window_observer_),
-      observed_removed_windows_(&removed_window_observer_),
-      observed_activation_clients_(this) {
-  // We can't assume all RootWindows have the same ActivationClient.
-  // Add a RootWindow and its ActivationClient to the observed list.
+      observed_removed_windows_(&removed_window_observer_) {
+  Shell::GetInstance()->activation_client()->AddObserver(this);

[James Cook, 2016/07/26 17:48:31]

This will get converted to WmShell in my next CL. I kept ash::Shell here to keep
this CL simpler.

   for (aura::Window* root : Shell::GetAllRootWindows())
     OnRootWindowAdded(WmWindowAura::Get(root));
 
@@ -117,6 +115,7 @@ ShelfWindowWatcher::ShelfWindowWatcher(ShelfModel* model)
 
 ShelfWindowWatcher::~ShelfWindowWatcher() {
   display::Screen::GetScreen()->RemoveObserver(this);
+  Shell::GetInstance()->activation_client()->RemoveObserver(this);
 }
 
 void ShelfWindowWatcher::AddShelfItem(aura::Window* window) {
@@ -139,10 +138,6 @@ void ShelfWindowWatcher::RemoveShelfItem(aura::Window* window) {
 
 void ShelfWindowWatcher::OnRootWindowAdded(WmWindow* root_window_wm) {
   aura::Window* root_window = WmWindowAura::GetAuraWindow(root_window_wm);
-  // |observed_activation_clients_| can have the same ActivationClient multiple
-  // times - which would be handled by the |observed_activation_clients_|.
-  observed_activation_clients_.Add(
-      aura::client::GetActivationClient(root_window));
   observed_root_windows_.Add(root_window);
 
   aura::Window* default_container =
@@ -154,8 +149,6 @@ void ShelfWindowWatcher::OnRootWindowAdded(WmWindow* root_window_wm) {
 
 void ShelfWindowWatcher::OnRootWindowRemoved(aura::Window* root_window) {
   observed_root_windows_.Remove(root_window);
-  observed_activation_clients_.Remove(
-      aura::client::GetActivationClient(root_window));
 }
 
 void ShelfWindowWatcher::UpdateShelfItemStatus(aura::Window* window,