Port touch-demo.sky to Dart and make it work in SkyShell

sky/shell/ui/input_event_converter.h

+// Copyright 2015 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.
+
+#ifndef SKY_SHELL_UI_INPUT_EVENT_CONVERTER_H_
+#define SKY_SHELL_UI_INPUT_EVENT_CONVERTER_H_
+
+#include "base/memory/scoped_ptr.h"
+#include "sky/services/viewport/input_event.mojom.h"
+
+namespace blink {
+class WebInputEvent;
+}
+
+namespace sky {
+
+scoped_ptr<blink::WebInputEvent> ConvertEvent(const InputEventPtr& event,
+                                              float device_pixel_ratio);
+}
+
+#endif  // SKY_SHELL_UI_INPUT_EVENT_CONVERTER_H_