[Android] Fix compilation error: unused variable 'kAllowedToAccessOnNonjoinableThread'

chrome/browser/metrics/thread_watcher_android.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 "chrome/browser/metrics/thread_watcher_android.h"
 
 #include "base/android/application_status_listener.h"
 #include "base/command_line.h"
 #include "base/lazy_instance.h"
 #include "chrome/browser/metrics/thread_watcher.h"
@@ skipping 21 matching lines @@
   } else if (application_state ==
              base::android::APPLICATION_STATE_HAS_RUNNING_ACTIVITIES &&
              g_application_has_stopped) {
     g_application_has_stopped = false;
     ThreadWatcherList::StartWatchingAll(*CommandLine::ForCurrentProcess());
   }
 }
 
 struct LeakyApplicationStatusListenerTraits {
   static const bool kRegisterOnExit = false;
+#ifndef NDEBUG
   static const bool kAllowedToAccessOnNonjoinableThread = true;
+#endif
 
   static base::android::ApplicationStatusListener* New(void* instance) {
     ANNOTATE_SCOPED_MEMORY_LEAK;
     return new (instance) base::android::ApplicationStatusListener(
             base::Bind(&OnApplicationStateChange));
   }
 
   static void Delete(base::android::ApplicationStatusListener* instance) {
   }
 };
 
 base::LazyInstance<base::android::ApplicationStatusListener,
                    LeakyApplicationStatusListenerTraits>
     g_application_status_listener = LAZY_INSTANCE_INITIALIZER;
 
 }  // namespace
 
 void ThreadWatcherAndroid::RegisterApplicationStatusListener() {
   // Leaky.
   g_application_status_listener.Get();
 }