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.
+    DLOG(WARNING) << "Creating dummy MessageLoop for AttachmentServiceProxy.";

[maniscalco, 2014/04/28 16:05:12]

I'm not real familiar with logging conventions in chrome, but would this be
better as info or some "low severity" log level since it's OK for a test to not
have a MessageLoop?

[tim (not reviewing), 2014/04/28 18:41:29]

Hmm, I'll make it a DVLOG(1).  I was worried that silently dealing with this
case might trip people up and wanted to shout about it.. but it's probably OK to
expect someone to turn on sync vlogging if things aren't working as expected, so
they'll see DVLOG(1).

+    base::MessageLoop loop;

[maniscalco, 2014/04/28 16:05:12]

Can you update the ASPFT class comment now that it no longer assumes a ML
already exists.

[tim (not reviewing), 2014/04/28 18:41:29]

Done.

+    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