Change Aura overlay scrollbars from solid color to painted scrollbars.

ui/native_theme/overlay_scrollbar_constants_aura.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 UI_NATIVE_THEME_OVERLAY_SCROLLBAR_CONSTANTS_AURA_H_
+#define UI_NATIVE_THEME_OVERLAY_SCROLLBAR_CONSTANTS_AURA_H_
+
+#include "base/time/time.h"
+#include "ui/gfx/skia_util.h"
+
+namespace ui {
+
+constexpr int kOverlayScrollbarThumbWidthNormal = 6;
+constexpr int kOverlayScrollbarThumbWidthHovered = 10;
+constexpr int kOverlayScrollbarThumbWidthPressed = 10;
+
+constexpr base::TimeDelta kOverlayScrollbarFadeOutDelay =
+    base::TimeDelta::FromMilliseconds(1000);
+constexpr base::TimeDelta kOverlayScrollbarFadeOutDuration =
+    base::TimeDelta::FromMilliseconds(200);
+// TODO(bokan): This is still undetermined. crbug.com/652520.
+constexpr base::TimeDelta kOverlayScrollbarThinningDuration =
+    base::TimeDelta::FromMilliseconds(200);
+
+} // namespace ui
+
+#endif // UI_NATIVE_THEME_OVERLAY_SCROLLBAR_CONSTANTS_AURA_H_