Fix dangling observer

mash/wm/user_window_controller_impl.cc

Index: mash/wm/user_window_controller_impl.cc
diff --git a/mash/wm/user_window_controller_impl.cc b/mash/wm/user_window_controller_impl.cc
index 1201d0bdbb88367ad311f5a5d6534bfdee3f5b66..de983c7c325de710937992044c3fcca234b080de 100644
--- a/mash/wm/user_window_controller_impl.cc
+++ b/mash/wm/user_window_controller_impl.cc
@@ -89,15 +89,11 @@ UserWindowControllerImpl::~UserWindowControllerImpl() {
   if (!root_controller_)
     return;
 
-  // TODO(msw): should really listen for user window container being destroyed
-  // and cleanup there.
   mus::Window* user_container = GetUserWindowContainer();
   if (!user_container)

[msw, 2016/05/18 17:36:56]

optional nit: invert and nest the RemoveObservers call.

     return;
 
-  user_container->RemoveObserver(this);
-  for (auto iter : user_container->children())
-    iter->RemoveObserver(window_property_observer_.get());
+  RemoveObservers(user_container);
 }
 
 void UserWindowControllerImpl::Initialize(
@@ -119,6 +115,13 @@ void UserWindowControllerImpl::AssignIdIfNecessary(mus::Window* window) {
     window->SetLocalProperty(kUserWindowIdKey, next_id_++);
 }
 
+void UserWindowControllerImpl::RemoveObservers(mus::Window* user_container) {
+  user_container->RemoveObserver(this);
+  user_container->connection()->RemoveObserver(this);
+  for (auto iter : user_container->children())
+    iter->RemoveObserver(window_property_observer_.get());
+}
+
 mus::Window* UserWindowControllerImpl::GetUserWindowById(uint32_t id) {
   for (mus::Window* window : GetUserWindowContainer()->children()) {
     if (window->GetLocalProperty(kUserWindowIdKey) == id)
@@ -147,6 +150,11 @@ void UserWindowControllerImpl::OnTreeChanging(const TreeChangeParams& params) {
   }
 }
 
+void UserWindowControllerImpl::OnWindowDestroying(mus::Window* window) {
+  if (window == GetUserWindowContainer())
+    RemoveObservers(window);
+}
+
 void UserWindowControllerImpl::OnWindowTreeFocusChanged(
     mus::Window* gained_focus,
     mus::Window* lost_focus) {