Fix thread safety issues with //components/upload_list.

components/upload_list/BUILD.gn

 # Copyright 2015 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.
 
 source_set("upload_list") {
   sources = [
     "crash_upload_list.cc",
     "crash_upload_list.h",
     "upload_list.cc",
     "upload_list.h",
   ]
 
   deps = [
     "//base",
   ]
 }
 
 source_set("unit_tests") {
   testonly = true
   sources = [
     "upload_list_unittest.cc",
   ]
 
   deps = [
     ":upload_list",
     "//base",
+    "//base/test:test_support",
     "//testing/gtest",
   ]
 }