PPAPI: Check for NULL dispatcher in PPP_VideoDecoder

ppapi/proxy/ppp_video_decoder_proxy.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 "ppapi/proxy/ppp_video_decoder_proxy.h"
 
 #include "ppapi/proxy/host_dispatcher.h"
 #include "ppapi/proxy/plugin_globals.h"
 #include "ppapi/proxy/plugin_resource_tracker.h"
 #include "ppapi/proxy/ppapi_messages.h"
@@ skipping 41 matching lines @@
   HostDispatcher::GetForInstance(instance)->Send(
       new PpapiMsg_PPPVideoDecoder_PictureReady(
           API_ID_PPP_VIDEO_DECODER_DEV, decoder_resource, *picture));
 }
 
 void NotifyError(PP_Instance instance, PP_Resource decoder,
                  PP_VideoDecodeError_Dev error) {
   HostResource decoder_resource;
   decoder_resource.SetHostResource(instance, decoder);
 
-  HostDispatcher::GetForInstance(instance)->Send(
+  // It's possible that the error we're being notified about is happening
+  // because the instance is shutting down. In this case, our instance may
+  // already have been removed from the HostDispatcher map.
+  HostDispatcher* dispatcher = HostDispatcher::GetForInstance(instance);
+  if (dispatcher) {
+    dispatcher->Send(
       new PpapiMsg_PPPVideoDecoder_NotifyError(
           API_ID_PPP_VIDEO_DECODER_DEV, decoder_resource, error));
+  }
 }
 
 static const PPP_VideoDecoder_Dev video_decoder_interface = {
   &ProvidePictureBuffers,
   &DismissPictureBuffer,
   &PictureReady,
   &NotifyError
 };
 
 InterfaceProxy* CreateVideoDecoderPPPProxy(Dispatcher* dispatcher) {
@@ skipping 94 matching lines @@
   if (!plugin_decoder)
     return;
   CallWhileUnlocked(ppp_video_decoder_impl_->NotifyError,
                     decoder.instance(),
                     plugin_decoder,
                     error);
 }
 
 }  // namespace proxy
 }  // namespace ppapi