Convert the async device ID getter to a chrome resource host

ppapi/host/ppapi_host.cc

Index: ppapi/host/ppapi_host.cc
diff --git a/ppapi/host/ppapi_host.cc b/ppapi/host/ppapi_host.cc
index 247c78184ff0e83b821fc84fea37432513673568..0ec37b6e11d2c8ac9ff5a7c96593a5420a1e310e 100644
--- a/ppapi/host/ppapi_host.cc
+++ b/ppapi/host/ppapi_host.cc
@@ -26,10 +26,8 @@ const size_t kMaxResourcesPerPlugin = 1 << 14;
 }  // namespace
 
 PpapiHost::PpapiHost(IPC::Sender* sender,
-                     HostFactory* host_factory,
                      const PpapiPermissions& perms)
     : sender_(sender),
-      host_factory_(host_factory),
       permissions_(perms) {
 }
 
@@ -73,6 +71,9 @@ void PpapiHost::SendReply(const proxy::ResourceMessageReplyParams& params,
   Send(new PpapiPluginMsg_ResourceReply(params, msg));
 }
 
+void PpapiHost::AddHostFactoryFilter(scoped_ptr<HostFactory> filter) {
+  host_factory_filters_.push_back(filter.release());
+}
 
 void PpapiHost::AddInstanceMessageFilter(
     scoped_ptr<InstanceMessageFilter> filter) {
@@ -121,8 +122,15 @@ void PpapiHost::OnHostMsgResourceCreated(
   if (resources_.size() >= kMaxResourcesPerPlugin)
     return;
 
-  scoped_ptr<ResourceHost> resource_host(
-      host_factory_->CreateResourceHost(this, params, instance, nested_msg));
+  // Run through all filters until one grabs this message.
+  scoped_ptr<ResourceHost> resource_host;
+  DCHECK(!host_factory_filters_.empty());  // Caller forgot to add a factory.
+  for (size_t i = 0; i < host_factory_filters_.size(); i++) {
+    resource_host = host_factory_filters_[i]->CreateResourceHost(
+        this, params, instance, nested_msg).Pass();
+    if (resource_host.get())
+      break;
+  }
   if (!resource_host.get()) {
     NOTREACHED();

[yzshen1, 2012/09/11 00:53:17]

According to the comment in resource_host.h
"Some (but not all) resources have a corresponding object in the host side"

So it seems okay to get NULL here.

[brettw, 2012/09/11 20:25:20]

If there isn't a corresponding host object, the proxy shouldn't be sending a
"created" message to the browser/renderer to create the host.

     return;