Fix AshWindowTreeHost shutdown for Ozone X11.

ui/platform_window/x11/x11_window_ozone.cc

 // Copyright 2016 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 "ui/platform_window/x11/x11_window_ozone.h"
 
 #include <X11/Xlib.h>
 
 #include "base/bind.h"
 #include "ui/events/event.h"
 #include "ui/events/ozone/events_ozone.h"
 #include "ui/events/platform/x11/x11_event_source.h"
 #include "ui/gfx/geometry/point.h"
 #include "ui/platform_window/x11/x11_cursor_ozone.h"
 #include "ui/platform_window/x11/x11_window_manager_ozone.h"
 
 namespace ui {
 
-X11WindowOzone::X11WindowOzone(X11EventSourceLibevent* event_source,
-                               X11WindowManagerOzone* window_manager,
+X11WindowOzone::X11WindowOzone(X11WindowManagerOzone* window_manager,
                                PlatformWindowDelegate* delegate,
                                const gfx::Rect& bounds)
-    : X11WindowBase(delegate, bounds),
-      event_source_(event_source),
-      window_manager_(window_manager) {
-  DCHECK(event_source_);
+    : X11WindowBase(delegate, bounds), window_manager_(window_manager) {
   DCHECK(window_manager);
-  event_source_->AddPlatformEventDispatcher(this);
-  event_source_->AddXEventDispatcher(this);
+  auto* event_source = X11EventSourceLibevent::GetInstance();
+  if (event_source) {
+    event_source->AddPlatformEventDispatcher(this);
+    event_source->AddXEventDispatcher(this);
+  }
 }
 
 X11WindowOzone::~X11WindowOzone() {
-  event_source_->RemovePlatformEventDispatcher(this);
-  event_source_->RemoveXEventDispatcher(this);
+  X11WindowOzone::PrepareForShutdown();
+}
+
+void X11WindowOzone::PrepareForShutdown() {
+  auto* event_source = X11EventSourceLibevent::GetInstance();
+  if (event_source) {
+    event_source->RemovePlatformEventDispatcher(this);
+    event_source->RemoveXEventDispatcher(this);
+  }
 }
 
 void X11WindowOzone::SetCapture() {
   window_manager_->GrabEvents(xwindow());
 }
 
 void X11WindowOzone::ReleaseCapture() {
   window_manager_->UngrabEvents(xwindow());
 }
 
@@ skipping 33 matching lines @@
 uint32_t X11WindowOzone::DispatchEvent(const PlatformEvent& platform_event) {
   // This is unfortunately needed otherwise events that depend on global state
   // (eg. double click) are broken.
   DispatchEventFromNativeUiEvent(
       platform_event, base::Bind(&PlatformWindowDelegate::DispatchEvent,
                                  base::Unretained(delegate())));
   return POST_DISPATCH_STOP_PROPAGATION;
 }
 
 }  // namespace ui