Complete SyncMessageFilter initialization after SyncChannel initialization

ipc/ipc_sync_message_filter.h

Index: ipc/ipc_sync_message_filter.h
diff --git a/ipc/ipc_sync_message_filter.h b/ipc/ipc_sync_message_filter.h
index 2a3c4e89a4c01bad945b7f341f6e0632f9fed1c2..6e4f991da633a4b56840d35b740232beaa38fc53 100644
--- a/ipc/ipc_sync_message_filter.h
+++ b/ipc/ipc_sync_message_filter.h
@@ -48,6 +48,10 @@ class IPC_EXPORT SyncMessageFilter : public MessageFilter, public Sender {
  private:
   friend class SyncChannel;
 
+  void set_is_channel_send_thread_safe(bool is_channel_send_thread_safe) {
+    is_channel_send_thread_safe_ = is_channel_send_thread_safe;
+  }
+
   void SendOnIOThread(Message* message);
   // Signal all the pending sends as done, used in an error condition.
   void SignalAllEvents();