Fix two crash and potential leak&crash

ash/accelerators/accelerator_dispatcher_linux.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/accelerators/accelerator_dispatcher.h"
 
 #include <X11/Xlib.h>
 
 // Xlib defines RootWindow
 #ifdef RootWindow
@@ skipping 10 matching lines @@
 
 namespace {
 
 const int kModifierMask = (ui::EF_SHIFT_DOWN |
                            ui::EF_CONTROL_DOWN |
                            ui::EF_ALT_DOWN);
 }  // namespace
 
 base::MessagePumpDispatcher::DispatchStatus AcceleratorDispatcher::Dispatch(
     XEvent* xev) {
+  if (!associated_window_)
+    return EVENT_QUIT;
   if (!associated_window_->CanReceiveEvents())
     return aura::RootWindow::GetInstance()->GetDispatcher()->Dispatch(xev);
 
   if (xev->type == KeyPress) {
     ash::AcceleratorController* accelerator_controller =
         ash::Shell::GetInstance()->accelerator_controller();
     ui::Accelerator accelerator(ui::KeyboardCodeFromNative(xev),
                                 ui::EventFlagsFromNative(xev) & kModifierMask);
     if (accelerator_controller && accelerator_controller->Process(accelerator))
       return EVENT_PROCESSED;
   }
   return nested_dispatcher_->Dispatch(xev);
 }
 
 }  // namespace ash