views: Add support for absolute positioned overlay views.

To test:
Run `cefclient.exe --use-views --hide-frame --hide-controls`
Add `--enable-chrome-runtime` for the same behavior using the Chrome location
bar instead of a text field.

libcef/browser/chrome/views/chrome_views_util.h

@@ -0,0 +1,20 @@
+// Copyright 2021 The Chromium Embedded Framework 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 CEF_LIBCEF_BROWSER_CHROME_VIEWS_CHROME_VIEWS_H_
+#define CEF_LIBCEF_BROWSER_CHROME_VIEWS_CHROME_VIEWS_H_
+#pragma once
+
+namespace views {
+class View;
+}
+
+namespace cef {
+
+// Returns true if |view| is a CefView.
+bool IsCefView(views::View* view);
+
+}  // namespace cef
+
+#endif  // CEF_LIBCEF_BROWSER_CHROME_VIEWS_CHROME_VIEWS_H_