Revert of Remove calls to MessageLoop::current() in ios.

ios/web/web_thread_impl.cc

 // Copyright 2014 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 "ios/web/web_thread_impl.h"
 
 #include <string>
 
 #include "base/atomicops.h"
 #include "base/bind.h"
@@ skipping 359 matching lines @@
 bool WebThread::CurrentlyOn(ID identifier) {
   // This shouldn't use MessageLoop::current() since it uses LazyInstance which
   // may be deleted by ~AtExitManager when a WorkerPool thread calls this
   // function.
   // http://crbug.com/63678
   base::ThreadRestrictions::ScopedAllowSingleton allow_singleton;
   WebThreadGlobals& globals = g_globals.Get();
   base::AutoLock lock(globals.lock);
   DCHECK(identifier >= 0 && identifier < ID_COUNT);
   return globals.threads[identifier] &&
-         globals.threads[identifier]->task_runner()->BelongsToCurrentThread();
+         globals.threads[identifier]->message_loop() ==
+             base::MessageLoop::current();
 }
 
 // static
 std::string WebThread::GetDCheckCurrentlyOnErrorMessage(ID expected) {
   std::string actual_name = base::PlatformThread::GetName();
   if (actual_name.empty())
     actual_name = "Unknown Thread";
 
   std::string result = "Must be called on ";
   result += GetThreadName(expected);
@@ skipping 108 matching lines @@
   AtomicWord* storage =
       reinterpret_cast<AtomicWord*>(&globals.thread_delegates[identifier]);
   AtomicWord old_pointer = base::subtle::NoBarrier_AtomicExchange(
       storage, reinterpret_cast<AtomicWord>(delegate));
 
   // This catches registration when previously registered.
   DCHECK(!delegate || !old_pointer);
 }
 
 }  // namespace web