Change Aura overlay scrollbars from solid color to painted scrollbars.

ui/native_theme/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/ui.gni")
 import("//testing/test.gni")
 
 component("native_theme") {
   sources = [
     "common_theme.cc",
@@ skipping 11 matching lines @@
     "native_theme_switches.cc",
     "native_theme_switches.h",
   ]
 
   if (use_aura) {
     sources += [
       "native_theme_aura.cc",
       "native_theme_aura.h",
       "native_theme_dark_aura.cc",
       "native_theme_dark_aura.h",
+      "overlay_scrollbar_constants_aura.h",
     ]
   }
 
   defines = [ "NATIVE_THEME_IMPLEMENTATION" ]
 
   deps = [
     "//base",
     "//base/third_party/dynamic_annotations",
     "//skia",
     "//ui/base",
@@ skipping 50 matching lines @@
   deps = [
     ":native_theme",
     "//base/test:run_all_unittests",
     "//base/test:test_support",
     "//skia:skia",
     "//testing/gtest",
     "//ui/base",
     "//ui/gfx/geometry:geometry",
   ]
 }