Ensure tests have an active task runner

chrome/browser/net/spdyproxy/data_reduction_proxy_chrome_settings_unittest.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 <string>
 
 #include "base/memory/scoped_ptr.h"
 #include "base/prefs/pref_registry_simple.h"
 #include "base/prefs/testing_pref_service.h"
 #include "chrome/browser/net/spdyproxy/data_reduction_proxy_chrome_settings.h"
@@ skipping 30 matching lines @@
             .SkipSettingsInitialization()
             .Build();
     config_ = test_context_->mock_config();
     drp_chrome_settings_->ResetConfigForTest(config_);
     dict_ = make_scoped_ptr(new base::DictionaryValue());
 
     PrefRegistrySimple* registry = test_context_->pref_service()->registry();
     registry->RegisterDictionaryPref(prefs::kProxy);
   }
 
+  base::MessageLoopForIO message_loop_;
   scoped_ptr<DataReductionProxyChromeSettings> drp_chrome_settings_;
   scoped_ptr<base::DictionaryValue> dict_;
   scoped_ptr<data_reduction_proxy::DataReductionProxyTestContext> test_context_;
   data_reduction_proxy::MockDataReductionProxyConfig* config_;
 };
 
 TEST_F(DataReductionProxyChromeSettingsTest, MigrateEmptyProxy) {
   EXPECT_CALL(*config_, ContainsDataReductionProxy(_)).Times(0);
   drp_chrome_settings_->MigrateDataReductionProxyOffProxyPrefs(
       test_context_->pref_service());
@@ skipping 38 matching lines @@
   base::DictionaryValue* value =
       (base::DictionaryValue*)test_context_->pref_service()->GetUserPref(
           prefs::kProxy);
   std::string mode;
   EXPECT_TRUE(value->GetString("mode", &mode));
   EXPECT_EQ("fixed_servers", mode);
   std::string server;
   EXPECT_TRUE(value->GetString("server", &server));
   EXPECT_EQ("http=https://youtube.com", server);
 }