Use ScopedTaskEnvironment instead of MessageLoopForUI in components tests.

components/history/core/test/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.
 
 static_library("test") {
   testonly = true
   sources = [
     "database_test_utils.cc",
     "database_test_utils.h",
     "fake_web_history_service.cc",
@@ skipping 11 matching lines @@
     "thumbnail-inl.h",
     "thumbnail.cc",
     "thumbnail.h",
     "thumbnail_ios.mm",
     "wait_top_sites_loaded_observer.cc",
     "wait_top_sites_loaded_observer.h",
   ]
 
   deps = [
     "//base",
+    "//base/test:test_support",
     "//components/history/core/browser",
     "//components/sync/protocol:protocol",
     "//net",
     "//sql",
     "//sql:test_support",
     "//testing/gtest",
     "//ui/gfx",
     "//url",
   ]
 
   if (is_ios) {
     sources -= [ "thumbnail.cc" ]
   }
 }