Let IndexedDBContextImpl create its own task runner

chrome/browser/browsing_data/browsing_data_indexed_db_helper_unittest.cc

 // Copyright (c) 2012 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 "chrome/browser/browsing_data/browsing_data_indexed_db_helper.h"
 
 #include "base/strings/utf_string_conversions.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "chrome/test/base/testing_profile.h"
 #include "content/public/browser/browser_context.h"
 #include "content/public/browser/storage_partition.h"
 #include "content/public/test/test_browser_thread_bundle.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace {
 
 class CannedBrowsingDataIndexedDBHelperTest : public testing::Test {
  public:
-  void SetUp() override {
-    IndexedDBContext()->SetTaskRunnerForTesting(
-        base::ThreadTaskRunnerHandle::Get().get());
-  }
-
   content::IndexedDBContext* IndexedDBContext() {
     return content::BrowserContext::GetDefaultStoragePartition(&profile_)->
         GetIndexedDBContext();
   }
 
  private:
   content::TestBrowserThreadBundle thread_bundle_;
   TestingProfile profile_;
 };
 
@@ skipping 40 matching lines @@
       new CannedBrowsingDataIndexedDBHelper(IndexedDBContext()));
 
   ASSERT_TRUE(helper->empty());
   helper->AddIndexedDB(origin1, description);
   ASSERT_TRUE(helper->empty());
   helper->AddIndexedDB(origin2, description);
   ASSERT_TRUE(helper->empty());
 }
 
 }  // namespace