Add a hang monitor for Pepper plugins

ppapi/proxy/dispatcher.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/dispatcher.h"
 
 #include <string.h>  // For memset.
 
 #include <map>
 
@@ skipping 32 matching lines @@
   }
   return proxy;
 }
 
 base::MessageLoopProxy* Dispatcher::GetIPCMessageLoop() {
   return delegate()->GetIPCMessageLoop();
 }
 
 void Dispatcher::AddIOThreadMessageFilter(
     IPC::ChannelProxy::MessageFilter* filter) {
+  // Our filter is refcounted. The channel will call the destruct method on the
+  // filter when the channel is done with it, so the corresponding Release()
+  // happens there.
   channel()->AddFilter(filter);
 }
 
 bool Dispatcher::OnMessageReceived(const IPC::Message& msg) {
   if (msg.routing_id() <= 0 || msg.routing_id() >= API_ID_COUNT) {
     OnInvalidMessageReceived();
     return true;
   }
 
   InterfaceProxy* proxy = GetInterfaceProxy(
       static_cast<ApiID>(msg.routing_id()));
   if (!proxy) {
     NOTREACHED();
     return true;
   }
   return proxy->OnMessageReceived(msg);
 }
 
 void Dispatcher::SetSerializationRules(
     VarSerializationRules* var_serialization_rules) {
   serialization_rules_ = var_serialization_rules;
 }
 
 void Dispatcher::OnInvalidMessageReceived() {
 }
 
 }  // namespace proxy
 }  // namespace ppapi