Use ScopedTaskEnvironment instead of MessageLoopForUI in components tests.

components/history/core/test/history_backend_db_base_test.cc

 // 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.
 
 #include "components/history/core/test/history_backend_db_base_test.h"
 
 #include "base/files/file_path.h"
 #include "base/location.h"
 #include "base/run_loop.h"
 #include "base/single_thread_task_runner.h"
@@ skipping 44 matching lines @@
                                       KeywordID keyword_id,
                                       const base::string16& term) override {}
   void NotifyKeywordSearchTermDeleted(URLID url_id) override {}
   void DBLoaded() override {}
 
  private:
   HistoryBackendDBBaseTest* history_test_;
 };
 
 HistoryBackendDBBaseTest::HistoryBackendDBBaseTest()
-    : db_(nullptr),
-      last_profile_error_ (sql::INIT_OK) {
-}
+    : scoped_task_environment_(
+          base::test::ScopedTaskEnvironment::MainThreadType::UI),
+      db_(nullptr),
+      last_profile_error_(sql::INIT_OK) {}
 
 HistoryBackendDBBaseTest::~HistoryBackendDBBaseTest() {
 }
 
 void HistoryBackendDBBaseTest::SetUp() {
   ASSERT_TRUE(temp_dir_.CreateUniqueTempDir());
   history_dir_ = temp_dir_.GetPath().AppendASCII("HistoryBackendDBBaseTest");
   ASSERT_TRUE(base::CreateDirectory(history_dir_));
 }
 
@@ skipping 56 matching lines @@
       GURL("http://tab-referrer-url.example.com/"), std::string(),
       "application/vnd.oasis.opendocument.text", "application/octet-stream",
       time, time, std::string(), std::string(), 0, 512, state,
       DownloadDangerType::NOT_DANGEROUS, kTestDownloadInterruptReasonNone,
       std::string(), id, guid, false, time, true, "by_ext_id", "by_ext_name",
       std::vector<DownloadSliceInfo>());
   return db_->CreateDownload(download);
 }
 
 }  // namespace history