Revert of Ensure BrowserThread::CurrentlyOn is correct through MessageLoop teardown

chrome/browser/safe_browsing/protocol_manager_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/safe_browsing/protocol_manager.h"
 
 #include <memory>
 #include <vector>
 
 #include "base/strings/stringprintf.h"
@@ skipping 56 matching lines @@
 
 }  // namespace
 
 namespace safe_browsing {
 
 class SafeBrowsingProtocolManagerTest : public testing::Test {
  protected:
   SafeBrowsingProtocolManagerTest()
       : runner_(new base::TestSimpleTaskRunner),
         runner_handler_(runner_),
-        io_thread_(content::BrowserThread::IO, base::MessageLoop::current()) {}
+        io_thread_(content::BrowserThread::IO) {}
 
   ~SafeBrowsingProtocolManagerTest() override {}
 
   void SetUp() override {
     std::string key = google_apis::GetAPIKey();
     if (!key.empty()) {
       key_param_ = base::StringPrintf(
           "&key=%s",
           net::EscapeQueryParamValue(key, true).c_str());
     }
@@ skipping 1010 matching lines @@
 
   EXPECT_FALSE(pm->IsUpdateScheduled());
 
   // Invoke the AddChunksCallback to finish the update.
   runner_->RunPendingTasks();
 
   EXPECT_TRUE(pm->IsUpdateScheduled());
 }
 
 }  // namespace safe_browsing