Support sync mojo IPCs to and from bindings running on a sequence.

mojo/public/cpp/bindings/lib/multiplex_router.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "mojo/public/cpp/bindings/lib/multiplex_router.h"
 
 #include <stdint.h>
 
 #include <utility>
 
@@ skipping 295 matching lines @@
                  std::move(runner)),
       lock_(config == MULTI_INTERFACE ? new base::Lock : nullptr),
       control_message_handler_(this),
       control_message_proxy_(&connector_),
       next_interface_id_value_(1),
       posted_to_process_tasks_(false),
       encountered_error_(false),
       paused_(false),
       testing_mode_(false) {
   DCHECK(task_runner_->RunsTasksOnCurrentThread());
-  DCHECK(config == SINGLE_INTERFACE || base::ThreadTaskRunnerHandle::IsSet());
 
   if (config == SINGLE_INTERFACE_WITH_SYNC_METHODS ||
       config == MULTI_INTERFACE) {
     // Always participate in sync handle watching in multi-interface mode,
     // because even if it doesn't expect sync requests during sync handle
     // watching, it may still need to dispatch messages to associated endpoints
     // on a different thread.
     connector_.AllowWokenUpBySyncWatchOnSameThread();
   }
   connector_.set_incoming_receiver(&filters_);
@@ skipping 610 matching lines @@
 
 void MultiplexRouter::AssertLockAcquired() {
 #if DCHECK_IS_ON()
   if (lock_)
     lock_->AssertAcquired();
 #endif
 }
 
 }  // namespace internal
 }  // namespace mojo