Make it possible to set the display mode from the WebView API

public/platform/WebDisplayMode.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 WebDisplayMode_h
+#define WebDisplayMode_h
+
+namespace blink {
+
+enum WebDisplayMode {
+    WebDisplayModeUndefined, // User for override setting (ie. not set).
+    WebDisplayModeBrowser,
+    WebDisplayModeMinimalUi,
+    WebDisplayModeStandalone,
+    WebDisplayModeFullscreen
+};
+
+} // namespace blink
+
+#endif // WebDisplayMode_h