FBTF: Fix more ctor/dtors found by clang plugin.

base/thread_checker.cc

 // Copyright (c) 2010 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/thread_checker.h"
 
 // This code is only done in debug builds.
 #ifndef NDEBUG
 
 ThreadChecker::ThreadChecker() {
   EnsureThreadIdAssigned();
 }
 
+ThreadChecker::~ThreadChecker() {}
+
 bool ThreadChecker::CalledOnValidThread() const {
   EnsureThreadIdAssigned();
   return *valid_thread_id_ == PlatformThread::CurrentId();
 }
 
 void ThreadChecker::DetachFromThread() {
   valid_thread_id_.reset();
 }
 
 void ThreadChecker::EnsureThreadIdAssigned() const {
   if (valid_thread_id_.get())
     return;
   valid_thread_id_.reset(new PlatformThreadId(PlatformThread::CurrentId()));
 }
 
 #endif  // NDEBUG