Fix cases where RunLoop is created without a MessageLoop.

base/run_loop.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/run_loop.h"
 
 #include "base/bind.h"
 #include "base/tracked_objects.h"
 #include "build/build_config.h"
 
 namespace base {
 
 RunLoop::RunLoop()
     : loop_(MessageLoop::current()),
       previous_run_loop_(NULL),
       run_depth_(0),
       run_called_(false),
       quit_called_(false),
       running_(false),
       quit_when_idle_received_(false),
       weak_factory_(this) {
+  DCHECK(loop_);
 }
 
 RunLoop::~RunLoop() {
 }
 
 void RunLoop::Run() {
   DCHECK(thread_checker_.CalledOnValidThread());
   if (!BeforeRun())
     return;
 
@@ skipping 59 matching lines @@
 
   // Pop RunLoop stack:
   loop_->run_loop_ = previous_run_loop_;
 
   // Execute deferred QuitNow, if any:
   if (previous_run_loop_ && previous_run_loop_->quit_called_)
     loop_->QuitNow();
 }
 
 }  // namespace base