Check internal display RootWindow before getting the compositor.

ash/wallpaper/wallpaper_controller.cc

Index: ash/wallpaper/wallpaper_controller.cc
diff --git a/ash/wallpaper/wallpaper_controller.cc b/ash/wallpaper/wallpaper_controller.cc
index 2991f51db0545ad44fd7796927d02d8112a4ec9a..dcd93e12b738bf30d16fdde883993de7b9092a06 100644
--- a/ash/wallpaper/wallpaper_controller.cc
+++ b/ash/wallpaper/wallpaper_controller.cc
@@ -416,14 +416,16 @@ bool WallpaperController::MoveToUnlockedContainer() {
 
 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));
+    }
   }
 }