sync: don't require a MessageLoopProxy in AttachmentServiceProxyForTest

sync/api/attachments/attachment_service_proxy_for_test.cc

Index: sync/api/attachments/attachment_service_proxy_for_test.cc
diff --git a/sync/api/attachments/attachment_service_proxy_for_test.cc b/sync/api/attachments/attachment_service_proxy_for_test.cc
index 7f9f873b289b4225e7b4b5696e37afc8fc4e5057..8826991429b0a0b7c32e5d9af47105183bc32081 100644
--- a/sync/api/attachments/attachment_service_proxy_for_test.cc
+++ b/sync/api/attachments/attachment_service_proxy_for_test.cc
@@ -4,6 +4,7 @@
 
 #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"
 
@@ -36,8 +37,16 @@ AttachmentServiceProxy AttachmentServiceProxyForTest::Create() {
 
   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() {