Don't dispatch PPP_VideoDecoder_Dev methods with no decoder.

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 107 matching lines @@
   return handled;
 }
 
 void PPP_VideoDecoder_Proxy::OnMsgProvidePictureBuffers(
     const HostResource& decoder,
     uint32_t req_num_of_bufs,
     const PP_Size& dimensions,
     uint32_t texture_target) {
   PP_Resource plugin_decoder = PluginGlobals::Get()->plugin_resource_tracker()->
       PluginResourceForHostResource(decoder);
+  if (!plugin_decoder)
+    return;
   CallWhileUnlocked(ppp_video_decoder_impl_->ProvidePictureBuffers,
                     decoder.instance(),
                     plugin_decoder,
                     req_num_of_bufs,
                     &dimensions,
                     texture_target);
 }
 
 void PPP_VideoDecoder_Proxy::OnMsgDismissPictureBuffer(
     const HostResource& decoder, int32_t picture_id) {
   PP_Resource plugin_decoder = PluginGlobals::Get()->plugin_resource_tracker()->
       PluginResourceForHostResource(decoder);
+  if (!plugin_decoder)
+    return;
   CallWhileUnlocked(ppp_video_decoder_impl_->DismissPictureBuffer,
                     decoder.instance(),
                     plugin_decoder,
                     picture_id);
 }
 
 void PPP_VideoDecoder_Proxy::OnMsgPictureReady(
     const HostResource& decoder, const PP_Picture_Dev& picture) {
   PP_Resource plugin_decoder = PluginGlobals::Get()->plugin_resource_tracker()->
       PluginResourceForHostResource(decoder);
+  if (!plugin_decoder)
+    return;
   CallWhileUnlocked(ppp_video_decoder_impl_->PictureReady,
                     decoder.instance(),
                     plugin_decoder,
                     &picture);
 }
 
 void PPP_VideoDecoder_Proxy::OnMsgNotifyError(
     const HostResource& decoder, PP_VideoDecodeError_Dev error) {
   PP_Resource plugin_decoder = PluginGlobals::Get()->plugin_resource_tracker()->
       PluginResourceForHostResource(decoder);
+  if (!plugin_decoder)
+    return;
   CallWhileUnlocked(ppp_video_decoder_impl_->NotifyError,
                     decoder.instance(),
                     plugin_decoder,
                     error);
 }
 
 }  // namespace proxy
 }  // namespace ppapi