ThreadWatcher: fix use-after-free bug.

chrome/browser/metrics/thread_watcher.h

 // 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.
 
 // This file defines a WatchDog thread that monitors the responsiveness of other
 // browser threads like UI, IO, DB, FILE and CACHED threads. It also defines
 // ThreadWatcher class which performs health check on threads that would like to
 // be watched. This file also defines ThreadWatcherList class that has list of
 // all active ThreadWatcher objects.
 //
@@ skipping 60 matching lines @@
 class StartupTimeBomb;
 class ThreadWatcherList;
 class ThreadWatcherObserver;
 
 // This class performs health check on threads that would like to be watched.
 class ThreadWatcher {
  public:
   // base::Bind supports methods with up to 6 parameters. WatchingParams is used
   // as a workaround that limitation for invoking ThreadWatcher::StartWatching.
   struct WatchingParams {
-    const content::BrowserThread::ID& thread_id;
-    const std::string& thread_name;
-    const base::TimeDelta& sleep_time;
-    const base::TimeDelta& unresponsive_time;
+    content::BrowserThread::ID thread_id;
+    std::string thread_name;
+    base::TimeDelta sleep_time;
+    base::TimeDelta unresponsive_time;
     uint32_t unresponsive_threshold;
     bool crash_on_hang;
     uint32_t live_threads_threshold;
 
     WatchingParams(const content::BrowserThread::ID& thread_id_in,
                    const std::string& thread_name_in,
                    const base::TimeDelta& sleep_time_in,
                    const base::TimeDelta& unresponsive_time_in,
                    uint32_t unresponsive_threshold_in,
                    bool crash_on_hang_in,
@@ skipping 592 matching lines @@
   // shutdown_watchdog_ watches for hangs during shutdown.
   base::Watchdog* shutdown_watchdog_;
 
   // The |thread_id_| on which this object is constructed.
   const base::PlatformThreadId thread_id_;
 
   DISALLOW_COPY_AND_ASSIGN(ShutdownWatcherHelper);
 };
 
 #endif  // CHROME_BROWSER_METRICS_THREAD_WATCHER_H_