Change Aura overlay scrollbars from solid color to painted scrollbars.

ui/native_theme/overlay_scrollbar_constants_aura.h

Index: ui/native_theme/overlay_scrollbar_constants_aura.h
diff --git a/ui/native_theme/overlay_scrollbar_constants_aura.h b/ui/native_theme/overlay_scrollbar_constants_aura.h
new file mode 100644
index 0000000000000000000000000000000000000000..9daa0d3a2bcc41b8814134c004bc12da90d8b24b
--- /dev/null
+++ b/ui/native_theme/overlay_scrollbar_constants_aura.h
@@ -0,0 +1,24 @@
+// 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 "ui/gfx/skia_util.h"
+
+namespace ui {
+
+constexpr int kOverlayScrollbarThumbWidthNormal = 6;
+constexpr int kOverlayScrollbarThumbWidthHovered = 10;
+constexpr int kOverlayScrollbarThumbWidthPressed = 10;
+
+constexpr int kOverlayScrollbarFadeOutDelayMs = 1000;
+constexpr int kOverlayScrollbarFadeOutDurationMs = 200;

[Peter Kasting, 2016/10/18 00:43:36]

Nit: Does it make sense to do something like this?

constexpr base::TimeDelta kOverlayScrollbarFadeOutDelay =
    base::TimeDelta::FromMilliseconds(1000);
constexpr base::TimeDelta kOverlayScrollbarFadeOutDuration =
    base::TimeDelta::FromMilliseconds(200);

This is more verbose, but it prevents misuse of these numbers by people not
reading the unit names.

Of course, this would depend on also plumbing these as TimeDeltas, not ints,
through the rest of the system.

[bokan, 2016/10/18 20:34:49]

Done + plumbing

+
+// TODO(bokan): This is still undetermined. crbug.com/652520.
+constexpr int kOverlayScrollbarThinningDurationMs = 200;
+
+} // namespace ui
+
+#endif // UI_NATIVE_THEME_OVERLAY_SCROLLBAR_CONSTANTS_AURA_H_