Replace MessageLoopProxy with ThreadTaskRunnerHandle in src/sync/.

sync/syncable/syncable_unittest.cc

Index: sync/syncable/syncable_unittest.cc
diff --git a/sync/syncable/syncable_unittest.cc b/sync/syncable/syncable_unittest.cc
index 227b406e2a15d07650313ad5a150e47924a6071d..ef0c9ddc93839dbd9ac54f17f1b9d27e1d64d349 100644
--- a/sync/syncable/syncable_unittest.cc
+++ b/sync/syncable/syncable_unittest.cc
@@ -124,6 +124,7 @@ TestDirectory::TestDirectory(Encryptor* encryptor,
 TestDirectory::~TestDirectory() { }
 
 TEST(OnDiskSyncableDirectory, FailInitialWrite) {
+  base::MessageLoop message_loop;

[maniscalco, 2014/07/09 18:53:40]

You may be wondering why the heck are we adding a MessageLoop here?

The root cause is a small difference in behavior between 
MessageLoopProxy::current() and ThreadTaskRunnerHandle::Get().  Deep down this
test case invokes WeakCore's ctor which calls TTRH::Get.  MLP::current will
happily return null when there is no ML, however, TTRH::Get will DCHECK.

   FakeEncryptor encryptor;
   TestUnrecoverableErrorHandler handler;
   base::ScopedTempDir temp_dir;