sync: don't require a MessageLoopProxy in AttachmentServiceProxyForTest

BUG=none
R=maniscalco@chromium.org, pavely@chromium.org

Review URL: https://codereview.chromium.org/254713003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@266898 0039d316-1c4b-4281-b951-d872f2087c98

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 +37,17 @@ 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.
+    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() {

sync/api/attachments/attachment_service_proxy_for_test.h

@@ -14,8 +14,9 @@ namespace syncer {
 
 // An self-contained AttachmentServiceProxy to reduce boilerplate code in tests.
 //
-// Constructs and owns an AttachmentService suitable for use in tests.  Assumes
-// the current thread has a MessageLoop.
+// Constructs and owns an AttachmentService suitable for use in tests.
+// NOTE: This class does not require the current thread to have a MessageLoop,
+// however all methods will effectively become no-op stubs in that case.
 class SYNC_EXPORT AttachmentServiceProxyForTest
     : public AttachmentServiceProxy {
  public: