Pass device scale factor from display to ws.

services/ui/ws/viewport_metrics.h

+// Copyright 2016 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 SERVICES_UI_WS_VIEWPORT_METRICS_H_
+#define SERVICES_UI_WS_VIEWPORT_METRICS_H_
+
+#include "ui/gfx/geometry/rect.h"
+#include "ui/gfx/geometry/size.h"
+
+namespace ui {
+namespace ws {
+
+struct ViewportMetrics {
+  gfx::Rect bounds;  // DIP.
+  gfx::Size pixel_size;
+  float device_scale_factor = 0.0f;
+};
+
+}  // namespace ws
+}  // namespace ui
+
+#endif  // SERVICES_UI_WS_VIEWPORT_METRICS_H_