Let IPC::SyncMessageFilter take advantage of thread-safe Send.

ipc/ipc_sync_channel.cc

Index: ipc/ipc_sync_channel.cc
diff --git a/ipc/ipc_sync_channel.cc b/ipc/ipc_sync_channel.cc
index 35b88a7edeb43a64ea0b37cf91b284c1ca0f8596..6ce1e99acf4c0ad93e25b81d16e50c4abf02da5f 100644
--- a/ipc/ipc_sync_channel.cc
+++ b/ipc/ipc_sync_channel.cc
@@ -460,6 +460,14 @@ void SyncChannel::SetRestrictDispatchChannelGroup(int group) {
   sync_context()->set_restrict_dispatch_group(group);
 }
 
+scoped_refptr<IPC::SyncMessageFilter> SyncChannel::AddNewSyncMessageFilter() {

[jam, 2015/08/04 23:06:41]

nit: usually functions that return a new objects start with Create.. AddNewFoo
sounds like a method that takes a newly constructed object and adds it to a
container.

CreateSyncMessageFilter() would be clearer i think, and the comment can say that
it also adds it.

[Ken Rockot(use gerrit already), 2015/08/04 23:55:44]

Done.

+  scoped_refptr<IPC::SyncMessageFilter> filter = new IPC::SyncMessageFilter(

[jam, 2015/08/04 23:06:41]

nit: no IPC::

[Ken Rockot(use gerrit already), 2015/08/04 23:55:45]

Done.

+      sync_context()->shutdown_event(),
+      sync_context()->IsChannelSendThreadSafe());
+  AddFilter(filter.get());
+  return filter;
+}
+
 bool SyncChannel::Send(Message* message) {
 #ifdef IPC_MESSAGE_LOG_ENABLED
   std::string name;