content: Add heartbeat trace for CategorizedWorkerPool.

base/synchronization/condition_variable.h

 // Copyright (c) 2011 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.
 
 // ConditionVariable wraps pthreads condition variable synchronization or, on
 // Windows, simulates it.  This functionality is very helpful for having
 // several threads wait for an event, as is common with a thread pool managed
 // by a master.  The meaning of such an event in the (worker) thread pool
 // scenario is that additional tasks are now available for processing.  It is
 // used in Chrome in the DNS prefetching system to notify worker threads that
@@ skipping 75 matching lines @@
 class BASE_EXPORT ConditionVariable {
  public:
   // Construct a cv for use with ONLY one user lock.
   explicit ConditionVariable(Lock* user_lock);
 
   ~ConditionVariable();
 
   // Wait() releases the caller's critical section atomically as it starts to
   // sleep, and the reacquires it when it is signaled.
   void Wait();
-  void TimedWait(const TimeDelta& max_time);
+  // TimedWait() returns true on timeout, otherwise returns false.
+  bool TimedWait(const TimeDelta& max_time);

[robliao, 2016/06/07 15:40:30]

Add a unit test to check this.

 
   // Broadcast() revives all waiting threads.
   void Broadcast();
   // Signal() revives one waiting thread.
   void Signal();
 
  private:
 
 #if defined(OS_WIN)
   CONDITION_VARIABLE cv_;
   SRWLOCK* const srwlock_;
 #elif defined(OS_POSIX)
   pthread_cond_t condition_;
   pthread_mutex_t* user_mutex_;
 #endif
 
 #if DCHECK_IS_ON() && (defined(OS_WIN) || defined(OS_POSIX))
   base::Lock* const user_lock_;  // Needed to adjust shadow lock state on wait.
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(ConditionVariable);
 };
 
 }  // namespace base
 
 #endif  // BASE_SYNCHRONIZATION_CONDITION_VARIABLE_H_