Update mojo sdk to rev f6c8ec07c01deebc13178d516225fd12695c3dc2

mojo/public/cpp/utility/lib/thread.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 "mojo/public/cpp/utility/thread.h"
 
 #include <assert.h>
 
 namespace mojo {
 
@@ skipping 31 matching lines @@
   rv = pthread_attr_destroy(&attr);
   assert(rv == 0);
 }
 
 void Thread::Join() {
   // Must have been started but not yet joined.
   assert(started_);
   assert(!joined_);
 
   joined_ = true;
-  int rv = pthread_join(thread_, NULL);
+  int rv = pthread_join(thread_, nullptr);
   MOJO_ALLOW_UNUSED_LOCAL(rv);
   assert(rv == 0);
 }
 
 // static
 void* Thread::ThreadRunTrampoline(void* arg) {
   Thread* self = static_cast<Thread*>(arg);
   self->Run();
-  return NULL;
+  return nullptr;
 }
 
 }  // namespace mojo