IPC: Delete thread-safe send support

ppapi/nacl_irt/manifest_service.cc

Index: ppapi/nacl_irt/manifest_service.cc
diff --git a/ppapi/nacl_irt/manifest_service.cc b/ppapi/nacl_irt/manifest_service.cc
index f045dbcb70428983b19bdc06f71a1a418ec20957..2a5d9bb02daf4e03a8608029d60210535b33ee3b 100644
--- a/ppapi/nacl_irt/manifest_service.cc
+++ b/ppapi/nacl_irt/manifest_service.cc
@@ -32,8 +32,7 @@ namespace ppapi {
 class ManifestMessageFilter : public IPC::SyncMessageFilter {
  public:
   ManifestMessageFilter(base::WaitableEvent* shutdown_event)
-      : SyncMessageFilter(shutdown_event,
-                          false /* is_channel_send_thread_safe */),
+      : SyncMessageFilter(shutdown_event),
         connected_event_(base::WaitableEvent::ResetPolicy::MANUAL,
                          base::WaitableEvent::InitialState::NOT_SIGNALED) {}