Never lock the Pepper proxy lock on the IO thread

ppapi/proxy/plugin_message_filter.cc

Index: ppapi/proxy/plugin_message_filter.cc
diff --git a/ppapi/proxy/plugin_message_filter.cc b/ppapi/proxy/plugin_message_filter.cc
index f2f1cbeef144475778d7119a4dcfc2b4d04d99b1..eaf526b95e5ec22d2cd87bc3b16a798387d8eb0e 100644
--- a/ppapi/proxy/plugin_message_filter.cc
+++ b/ppapi/proxy/plugin_message_filter.cc
@@ -54,6 +54,11 @@ bool PluginMessageFilter::Send(IPC::Message* msg) {
   return false;
 }
 
+void PluginMessageFilter::AddResourceMessageFilter(
+      const scoped_refptr<ResourceMessageFilter>& filter) {
+  resource_filters_.push_back(filter);
+}
+
 // static
 void PluginMessageFilter::DispatchResourceReplyForTest(
     const ResourceMessageReplyParams& reply_params,
@@ -82,17 +87,15 @@ void PluginMessageFilter::OnMsgReserveInstanceId(PP_Instance instance,
 void PluginMessageFilter::OnMsgResourceReply(
     const ResourceMessageReplyParams& reply_params,
     const IPC::Message& nested_msg) {
+  for (const auto& filter_ptr : resource_filters_) {
+    if (filter_ptr->OnResourceReplyReceived(reply_params, nested_msg))
+      return;
+  }
   scoped_refptr<base::MessageLoopProxy> target =
       resource_reply_thread_registrar_->GetTargetThread(reply_params,
                                                         nested_msg);
-
-  if (!target.get()) {
-    DispatchResourceReply(reply_params, nested_msg);

[raymes, 2015/03/03 03:07:44]

Why can we remove this check?

[dmichael (off chromium), 2015/03/03 18:27:56]

This was a special case in Yuzhu's version to allow handling an event on the IO
thread. I'm removing that capability in this CL, because I don't want us to ever
acquire the ProxyLock on the IO thread (see DispatchResourceReply below).

Also in this change: 
https://codereview.chromium.org/869883003/diff/300001/ppapi/proxy/resource_re...

-  } else {
-    target->PostTask(
-        FROM_HERE,
-        base::Bind(&DispatchResourceReply, reply_params, nested_msg));
-  }
+  target->PostTask(
+      FROM_HERE, base::Bind(&DispatchResourceReply, reply_params, nested_msg));
 }
 
 // static