Adds ability to suspend notifying observers when display list is changed

ash/mus/window_manager.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 "ash/mus/window_manager.h"
 
 #include <stdint.h>
 
 #include <utility>
 
@@ skipping 119 matching lines @@
   observers_.AddObserver(observer);
 }
 
 void WindowManager::RemoveObserver(WindowManagerObserver* observer) {
   observers_.RemoveObserver(observer);
 }
 
 RootWindowController* WindowManager::CreateRootWindowController(
     ui::Window* window,
     const display::Display& display) {
+  // CreateRootWindowController() means a new display is being added, so the
+  // DisplayList needs to be updated. Calling AddDisplay() results in
+  // notifying DisplayObservers. Ash code assumes when this happens their is

[James Cook, 2016/09/29 04:15:05]

nit: their -> there

[sky, 2016/09/29 18:04:44]

Done.

+  // a valid RootWindowController for the new display. Suspend notifying
+  // observers, add the Display, create the RootWindowController, and then
+  // notify DisplayObservers. Classic ash does this by making sure
+  // WindowTreeHostManager is added as a DisplayObserver early on.
+  std::unique_ptr<display::DisplayListObserverLock> display_lock =
+      screen_->display_list()->SuspendObserverUpdates();
+  const bool was_displays_empty = screen_->display_list()->displays().empty();

[James Cook, 2016/09/29 04:15:05]

optional: |is_first_display| ?

[sky, 2016/09/29 18:04:44]

Done.

   // TODO(sky): should be passed whether display is primary.

[James Cook, 2016/09/29 04:15:05]

Is this todo still relevant?

[sky, 2016/09/29 18:04:44]

I *think* so, but I'm not 100% positive. I'm not sure if a new display can be
added and made primary in one distinct step.

-
-  // There needs to be at least one display before creating
-  // RootWindowController, otherwise initializing the compositor fails.
-  const bool was_displays_empty = screen_->display_list()->displays().empty();
-  if (was_displays_empty) {
-    screen_->display_list()->AddDisplay(display,
-                                        display::DisplayList::Type::PRIMARY);
-  }
+  screen_->display_list()->AddDisplay(
+      display, was_displays_empty ? display::DisplayList::Type::PRIMARY
+                                  : display::DisplayList::Type::NOT_PRIMARY);
 
   std::unique_ptr<RootWindowController> root_window_controller_ptr(
       new RootWindowController(this, window, display));
   RootWindowController* root_window_controller =
       root_window_controller_ptr.get();
   root_window_controllers_.insert(std::move(root_window_controller_ptr));
 
   FOR_EACH_OBSERVER(WindowManagerObserver, observers_,
                     OnRootWindowControllerAdded(root_window_controller));
 
-  if (!was_displays_empty) {
-    // If this isn't the initial display then add the display to Screen after
-    // creating the RootWindowController. We need to do this after creating the
-    // RootWindowController as adding the display triggers OnDisplayAdded(),
-    // which triggers some overrides asking for the RootWindowController for the
-    // new display.
-    screen_->display_list()->AddDisplay(
-        display, display::DisplayList::Type::NOT_PRIMARY);
-  }
   return root_window_controller;
 }
 
 void WindowManager::DestroyRootWindowController(
     RootWindowController* root_window_controller) {
   if (root_window_controllers_.size() > 1) {
     DCHECK_NE(root_window_controller, GetPrimaryRootWindowController());
     root_window_controller->wm_root_window_controller()->MoveWindowsTo(
         WmWindowMus::Get(GetPrimaryRootWindowController()->root()));
   }
@@ skipping 150 matching lines @@
                                                     const ui::Event& event) {
   auto iter = accelerator_handlers_.find(GetAcceleratorNamespaceId(id));
   if (iter == accelerator_handlers_.end())
     return ui::mojom::EventResult::HANDLED;
 
   return iter->second->OnAccelerator(id, event);
 }
 
 }  // namespace mus
 }  // namespace ash