Ensure tests have an active task runner

chrome/browser/prefs/pref_model_associator_unittest.cc

 // Copyright (c) 2011 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 "base/memory/scoped_ptr.h"
 #include "base/prefs/scoped_user_pref_update.h"
 #include "base/values.h"
 #include "chrome/browser/prefs/pref_model_associator.h"
 #include "chrome/common/pref_names.h"
 #include "chrome/test/base/testing_profile.h"
+#include "content/public/test/test_browser_thread_bundle.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 class AbstractPreferenceMergeTest : public testing::Test {
  protected:
   void SetUp() override { pref_service_ = profile_.GetPrefs(); }
 
   void SetContentPattern(base::DictionaryValue* patterns_dict,
                          const std::string& expression,
                          const std::string& content_type,
                          int setting) {
@@ skipping 17 matching lines @@
     base::Value::Type type = pref->GetType();
     if (type == base::Value::TYPE_DICTIONARY)
       empty_value.reset(new base::DictionaryValue);
     else if (type == base::Value::TYPE_LIST)
       empty_value.reset(new base::ListValue);
     else
       FAIL();
     pref_service_->Set(pref_name.c_str(), *empty_value);
   }
 
+  content::TestBrowserThreadBundle thread_bundle_;
   TestingProfile profile_;
   PrefService* pref_service_;
 };
 
 class ListPreferenceMergeTest : public AbstractPreferenceMergeTest {
  protected:
   ListPreferenceMergeTest() :
       server_url0_("http://example.com/server0"),
       server_url1_("http://example.com/server1"),
       local_url0_("http://example.com/local0"),
@@ skipping 352 matching lines @@
   std::string expression0_;
   std::string expression1_;
   std::string content_type0_;
   base::ListValue server_url_list_;
   base::DictionaryValue server_patterns_;
 };
 
 TEST_F(IndividualPreferenceMergeTest, URLsToRestoreOnStartup) {
   EXPECT_TRUE(MergeListPreference(prefs::kURLsToRestoreOnStartup));
 }