Make reftests work for sky.

sky/compositor/display_delegate.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 "sky/compositor/display_delegate.h"
+
+namespace sky {
+
+static CreateDisplayDelegate createDisplayDelegateFunction = 0;
+
+void DisplayDelegate::setDisplayDelegateCreateFunction(CreateDisplayDelegate createFunction)
+{
+    DCHECK(createFunction);
+    DCHECK(!createDisplayDelegateFunction);
+    createDisplayDelegateFunction = createFunction;
+}
+
+DisplayDelegate* DisplayDelegate::create(LayerClient* client)
+{
+    DCHECK(createDisplayDelegateFunction);
+    return createDisplayDelegateFunction(client);
+}
+
+}  // namespace sky