Remove unused paintScrollbarThumb impl.

content/shell/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/features.gni")
 import("//build/config/ui.gni")
 import("//tools/grit/repack.gni")
 import("//tools/grit/grit_rule.gni")
 if (is_android) {
   import("//build/config/android/config.gni")
@@ skipping 158 matching lines @@
     "renderer/test_runner/mock_web_media_stream_center.cc",
     "renderer/test_runner/mock_web_media_stream_center.h",
     "renderer/test_runner/mock_web_midi_accessor.cc",
     "renderer/test_runner/mock_web_midi_accessor.h",
     "renderer/test_runner/mock_web_push_client.cc",
     "renderer/test_runner/mock_web_push_client.h",
     "renderer/test_runner/mock_web_speech_recognizer.cc",
     "renderer/test_runner/mock_web_speech_recognizer.h",
     "renderer/test_runner/mock_web_theme_engine.cc",
     "renderer/test_runner/mock_web_theme_engine.h",
-    "renderer/test_runner/mock_web_theme_engine_mac.h",
-    "renderer/test_runner/mock_web_theme_engine_mac.mm",
     "renderer/test_runner/mock_web_user_media_client.cc",
     "renderer/test_runner/mock_web_user_media_client.h",
     "renderer/test_runner/mock_webrtc_data_channel_handler.cc",
     "renderer/test_runner/mock_webrtc_data_channel_handler.h",
     "renderer/test_runner/mock_webrtc_dtmf_sender_handler.cc",
     "renderer/test_runner/mock_webrtc_dtmf_sender_handler.h",
     "renderer/test_runner/mock_webrtc_peer_connection_handler.cc",
     "renderer/test_runner/mock_webrtc_peer_connection_handler.h",
     "renderer/test_runner/notification_presenter.cc",
     "renderer/test_runner/notification_presenter.h",
@@ skipping 295 matching lines @@
   if (is_android && !is_android_webview_build) {
     # Some tests rely on this tool. It might be nicer if these tests relied on
     # image diff rather than having content shell depend on it.
     datadeps = [
       "//tools/imagediff($host_toolchain)",
     ]
   }
 }
 
 }