Revert of PPAPI: Never re-enter JavaScript for PostMessage.

ppapi/proxy/host_dispatcher.cc

Index: ppapi/proxy/host_dispatcher.cc
diff --git a/ppapi/proxy/host_dispatcher.cc b/ppapi/proxy/host_dispatcher.cc
index 69de02a6677c6f0407fd625f9c736f7f9e5a2880..8f3833f5ddff7fa8f6a8cec321b59911f77b60bb 100644
--- a/ppapi/proxy/host_dispatcher.cc
+++ b/ppapi/proxy/host_dispatcher.cc
@@ -61,8 +61,10 @@
 
 HostDispatcher::HostDispatcher(PP_Module module,
                                PP_GetInterface_Func local_get_interface,
+                               SyncMessageStatusReceiver* sync_status,
                                const PpapiPermissions& permissions)
     : Dispatcher(local_get_interface, permissions),
+      sync_status_(sync_status),
       pp_module_(module),
       ppb_proxy_(NULL),
       allow_plugin_reentrancy_(false) {
@@ -92,6 +94,8 @@
   if (!Dispatcher::InitWithChannel(delegate, peer_pid, channel_handle,
                                    is_client))
     return false;
+  AddIOThreadMessageFilter(sync_status_.get());
+
   Send(new PpapiMsg_SetPreferences(preferences));
   return true;
 }
@@ -153,11 +157,9 @@
     // destroys the plugin module and in turn the dispatcher.
     ScopedModuleReference scoped_ref(this);
 
-    FOR_EACH_OBSERVER(SyncMessageStatusObserver, sync_status_observer_list_,
-                      BeginBlockOnSyncMessage());
+    sync_status_->BeginBlockOnSyncMessage();
     bool result = Dispatcher::Send(msg);
-    FOR_EACH_OBSERVER(SyncMessageStatusObserver, sync_status_observer_list_,
-                      EndBlockOnSyncMessage());
+    sync_status_->EndBlockOnSyncMessage();
 
     return result;
   } else {
@@ -236,16 +238,6 @@
   if (iter->second)
     return proxied_interface;
   return NULL;
-}
-
-void HostDispatcher::AddSyncMessageStatusObserver(
-    SyncMessageStatusObserver* obs) {
-  sync_status_observer_list_.AddObserver(obs);
-}
-
-void HostDispatcher::RemoveSyncMessageStatusObserver(
-    SyncMessageStatusObserver* obs) {
-  sync_status_observer_list_.RemoveObserver(obs);
 }
 
 void HostDispatcher::AddFilter(IPC::Listener* listener) {