cros: Fix clusterfuzz crash when spawning app list very early in startup

ash/common/accelerators/accelerator_controller.cc

Index: ash/common/accelerators/accelerator_controller.cc
diff --git a/ash/common/accelerators/accelerator_controller.cc b/ash/common/accelerators/accelerator_controller.cc
index db032bb3a8cafe407d68f3628775a7d7165a25af..8e6c3c529bf8e8b55016d0f84d7a94a05e66551c 100644
--- a/ash/common/accelerators/accelerator_controller.cc
+++ b/ash/common/accelerators/accelerator_controller.cc
@@ -269,6 +269,13 @@ void HandleSwitchIme(ImeControlDelegate* ime_control_delegate,
 
 bool CanHandleToggleAppList(const ui::Accelerator& accelerator,
                             const ui::Accelerator& previous_accelerator) {
+  // Some tests try to spawn the app list before the shelf is created, but the
+  // app list depends on the shelf for positioning. Users never open the app

[msw, 2017/01/05 00:41:34]

The app list doesn't actually depend on the shelf for positioning (at least not
in practice anymore, afaik...). Perhaps we can remove any vestiges of that
dependency to avoid this crash?

+  // list that early, so disable showing it. http://crbug.com/676843
+  WmWindow* target_root = WmShell::Get()->GetRootWindowForNewWindows();
+  if (!WmShelf::ForWindow(target_root)->IsShelfInitialized())
+    return false;
+
   if (accelerator.key_code() == ui::VKEY_LWIN) {
     // If something else was pressed between the Search key (LWIN)
     // being pressed and released, then ignore the release of the