sync: don't require a MessageLoopProxy in AttachmentServiceProxyForTest

sync/api/attachments/attachment_service_proxy_for_test.cc

 // Copyright 2014 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 "sync/api/attachments/attachment_service_proxy_for_test.h"
 
+#include "base/message_loop/message_loop.h"
 #include "base/message_loop/message_loop_proxy.h"
 #include "sync/api/attachments/fake_attachment_service.h"
 
 namespace syncer {
 
 AttachmentServiceProxyForTest::OwningCore::OwningCore(
     scoped_ptr<AttachmentService> wrapped,
     scoped_ptr<base::WeakPtrFactory<AttachmentService> > weak_ptr_factory)
     : Core(weak_ptr_factory->GetWeakPtr()),
       wrapped_(wrapped.Pass()),
@@ skipping 12 matching lines @@
   // invoked before any of this class's members are initialized, we create the
   // WeakPtrFactory here and pass it to the ctor so that it may initialize its
   // base class and own the WeakPtrFactory.
   //
   // We must pass by scoped_ptr because WeakPtrFactory has no copy constructor.
   scoped_ptr<base::WeakPtrFactory<AttachmentService> > weak_ptr_factory(
       new base::WeakPtrFactory<AttachmentService>(wrapped.get()));
 
   scoped_refptr<Core> core_for_test(
       new OwningCore(wrapped.Pass(), weak_ptr_factory.Pass()));
-  return AttachmentServiceProxyForTest(base::MessageLoopProxy::current(),
-                                       core_for_test);
+
+  scoped_refptr<base::SequencedTaskRunner> runner(
+      base::MessageLoopProxy::current());
+  if (!runner) {
+    // Dummy runner for tests that don't care about AttachmentServiceProxy.
+    DVLOG(1) << "Creating dummy MessageLoop for AttachmentServiceProxy.";
+    base::MessageLoop loop;
+    // This works because |runner| takes a ref to the proxy.
+    runner = loop.message_loop_proxy();
+  }
+  return AttachmentServiceProxyForTest(runner, core_for_test);
 }
 
 AttachmentServiceProxyForTest::~AttachmentServiceProxyForTest() {
 }
 
 AttachmentServiceProxyForTest::AttachmentServiceProxyForTest(
     const scoped_refptr<base::SequencedTaskRunner>& wrapped_task_runner,
     const scoped_refptr<Core>& core)
     : AttachmentServiceProxy(wrapped_task_runner, core) {
 }
 
 }  // namespace syncer