Fix dangling observer

mash/wm/user_window_controller_impl.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "mash/wm/user_window_controller_impl.h"
 
 #include "components/mus/public/cpp/property_type_converters.h"
 #include "components/mus/public/cpp/window.h"
 #include "components/mus/public/cpp/window_property.h"
 #include "components/mus/public/cpp/window_tree_connection.h"
@@ skipping 71 matching lines @@
   DISALLOW_COPY_AND_ASSIGN(WindowPropertyObserver);
 };
 
 UserWindowControllerImpl::UserWindowControllerImpl()
     : root_controller_(nullptr) {}
 
 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(
     RootWindowController* root_controller) {
   DCHECK(root_controller);
   DCHECK(!root_controller_);
   root_controller_ = root_controller;
   GetUserWindowContainer()->AddObserver(this);
   GetUserWindowContainer()->connection()->AddObserver(this);
   window_property_observer_.reset(new WindowPropertyObserver(this));
   for (mus::Window* window : GetUserWindowContainer()->children()) {
     AssignIdIfNecessary(window);
     window->AddObserver(window_property_observer_.get());
   }
 }
 
 void UserWindowControllerImpl::AssignIdIfNecessary(mus::Window* window) {
   if (window->GetLocalProperty(kUserWindowIdKey) == 0u)
     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)
       return window;
   }
   return nullptr;
 }
 
 mus::Window* UserWindowControllerImpl::GetUserWindowContainer() const {
   return root_controller_->GetWindowForContainer(
       mojom::Container::USER_PRIVATE_WINDOWS);
 }
 
 void UserWindowControllerImpl::OnTreeChanging(const TreeChangeParams& params) {
   DCHECK(root_controller_);
   if (params.new_parent == GetUserWindowContainer()) {
     params.target->AddObserver(window_property_observer_.get());
     AssignIdIfNecessary(params.target);
     if (user_window_observer_)
       user_window_observer_->OnUserWindowAdded(GetUserWindow(params.target));
   } else if (params.old_parent == GetUserWindowContainer()) {
     params.target->RemoveObserver(window_property_observer_.get());
     if (user_window_observer_)
       user_window_observer_->OnUserWindowRemoved(
           params.target->GetLocalProperty(kUserWindowIdKey));
   }
 }
 
+void UserWindowControllerImpl::OnWindowDestroying(mus::Window* window) {
+  if (window == GetUserWindowContainer())
+    RemoveObservers(window);
+}
+
 void UserWindowControllerImpl::OnWindowTreeFocusChanged(
     mus::Window* gained_focus,
     mus::Window* lost_focus) {
   if (!user_window_observer_)
     return;
 
   // Treat focus in the user window hierarchy as focus of the top-level window.
   gained_focus = GetTopLevelWindow(gained_focus, GetUserWindowContainer());
   lost_focus = GetTopLevelWindow(lost_focus, GetUserWindowContainer());
   if (gained_focus == lost_focus)
@@ skipping 23 matching lines @@
 }
 
 void UserWindowControllerImpl::FocusUserWindow(uint32_t window_id) {
   mus::Window* window = GetUserWindowById(window_id);
   if (window)
     window->SetFocus();
 }
 
 }  // namespace wm
 }  // namespace mash