Check internal display RootWindow before getting the compositor.

ash/wallpaper/wallpaper_controller.cc

 // Copyright (c) 2012 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/wallpaper/wallpaper_controller.h"
 
 #include <string>
 #include <utility>
 
 #include "ash/ash_switches.h"
@@ skipping 398 matching lines @@
 bool WallpaperController::MoveToUnlockedContainer() {
   if (!locked_)
     return false;
 
   locked_ = false;
   return ReparentWallpaper(GetWallpaperContainerId(false));
 }
 
 void WallpaperController::GetInternalDisplayCompositorLock() {
   if (display::Display::HasInternalDisplay()) {
-    compositor_lock_ =
-        Shell::Get()
-            ->window_tree_host_manager()
-            ->GetRootWindowForDisplayId(display::Display::InternalDisplayId())
-            ->layer()
-            ->GetCompositor()
-            ->GetCompositorLock(this, base::TimeDelta::FromMilliseconds(
-                                          kCompositorLockTimeoutMs));
+    WmWindow* root_window = ShellPort::Get()->GetRootWindowForDisplayId(
+        display::Display::InternalDisplayId());
+    if (root_window) {
+      compositor_lock_ =
+          root_window->aura_window()

[oshima, 2017/05/11 22:29:26]

GetLayer()

[wutao, 2017/05/11 22:39:28]

Done.

+              ->layer()
+              ->GetCompositor()
+              ->GetCompositorLock(this, base::TimeDelta::FromMilliseconds(
+                                            kCompositorLockTimeoutMs));
+    }
   }
 }
 
 void WallpaperController::CompositorLockTimedOut() {
   compositor_lock_.reset();
 }
 
 }  // namespace ash