Fix Thread::SetMessageLoop(nullptr).

base/threading/thread.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 "base/threading/thread.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/lazy_instance.h"
 #include "base/location.h"
@@ skipping 243 matching lines @@
 bool Thread::GetThreadWasQuitProperly() {
   bool quit_properly = true;
 #ifndef NDEBUG
   quit_properly = lazy_tls_bool.Pointer()->Get();
 #endif
   return quit_properly;
 }
 
 void Thread::SetMessageLoop(MessageLoop* message_loop) {
   DCHECK(owning_sequence_checker_.CalledOnValidSequence());
-
-  // TODO(gab): Figure out why some callers pass in a null |message_loop|...
-  // https://crbug.com/629139#c15
-  // DCHECK(message_loop);
-  if (!message_loop)
-    return;
+  DCHECK(message_loop);
 
   // Setting |message_loop_| should suffice for this thread to be considered
   // as "running", until Stop() is invoked.
   DCHECK(!IsRunning());
   message_loop_ = message_loop;
   DCHECK(IsRunning());
 
   using_external_message_loop_ = true;
 }
 
@@ skipping 77 matching lines @@
   run_loop_ = nullptr;
 }
 
 void Thread::ThreadQuitHelper() {
   DCHECK(run_loop_);
   run_loop_->QuitWhenIdle();
   SetThreadWasQuitProperly(true);
 }
 
 }  // namespace base