Plumb resize notifications around sky/shell

sky/shell/ui_delegate.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_DELEGATE_H_
+#define SKY_SHELL_UI_DELEGATE_H_
+
+#include "ui/gfx/geometry/size.h"
+
+namespace sky {
+namespace shell {
+
+class UIDelegate {
+ public:
+  virtual void OnViewportMetricsChanged(const gfx::Size& size,
+                                        float device_pixel_ratio) = 0;
+
+ protected:
+  virtual ~UIDelegate();
+};
+
+}  // namespace shell
+}  // namespace sky
+
+#endif  // SKY_SHELL_UI_DELEGATE_H_