Implement --ozone-platform flag to select OzonePlatform implementation at runtime

ui/ozone/ozone_platform_list.h

+// Copyright (c) 2013 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 UI_OZONE_OZONE_PLATFORM_LIST_H_
+#define UI_OZONE_OZONE_PLATFORM_LIST_H_
+
+namespace ui {
+
+class OzonePlatform;
+
+typedef OzonePlatform* (*OzonePlatformConstructor)();
+
+struct OzonePlatformListEntry {
+  const char* name;
+  OzonePlatformConstructor constructor;
+};
+
+extern const OzonePlatformListEntry kOzonePlatforms[];
+
+extern const int kOzonePlatformCount;
+
+}  // namespace ui
+
+#endif  // UI_OZONE_OZONE_PLATFORM_LIST_H_