Implements a display scale tray setting behind a chrome switch

ash/system/display_scale/scale_view.h

Index: ash/system/display_scale/scale_view.h
diff --git a/ash/system/display_scale/scale_view.h b/ash/system/display_scale/scale_view.h
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index 0000000000000000000000000000000000000000..9f77c8a0f4ec294d34696800b68becdba543cc74
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+++ b/ash/system/display_scale/scale_view.h
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+// Copyright 2017 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 ASH_SYSTEM_DISPLAY_SCALE_SCALE_VIEW_H_
+#define ASH_SYSTEM_DISPLAY_SCALE_SCALE_VIEW_H_
+
+#include "base/macros.h"
+#include "ui/views/controls/button/button.h"
+#include "ui/views/controls/slider.h"
+#include "ui/views/view.h"
+
+namespace views {
+class CustomButton;
+class Label;
+}
+
+namespace ash {
+class SystemTrayItem;
+class TriView;
+
+namespace tray {
+class ScaleView : public views::View,
+                  public views::SliderListener,
+                  public views::ButtonListener {
+ public:
+  ScaleView(SystemTrayItem* owner, bool is_default_view);
+
+  ~ScaleView() override;
+
+ private:
+  // SliderListener:
+  void SliderValueChanged(views::Slider* sender,
+                          float value,
+                          float old_value,
+                          views::SliderChangeReason reason) override;
+  void SliderDragEnded(views::Slider* sender) override;
+
+  // views::ButtonListener:
+  void ButtonPressed(views::Button* sender, const ui::Event& event) override;
+
+  SystemTrayItem* owner_;
+  // The only immediate child view of |this|. All other view elements are added
+  // to the |tri_view_| to handle layout.
+  TriView* tri_view_;
+  views::CustomButton* more_button_;
+  views::Label* label_;
+  views::Slider* slider_;
+  bool is_default_view_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScaleView);
+};
+
+}  // namespace tray
+}  // namespace ash
+
+#endif  // ASH_SYSTEM_DISPLAY_SCALE_SCALE_VIEW_H_