Flush SequenceWorkerPool tasks after each unit test.

base/threading/sequenced_worker_pool.cc

Index: base/threading/sequenced_worker_pool.cc
===================================================================
--- base/threading/sequenced_worker_pool.cc	(revision 174239)
+++ base/threading/sequenced_worker_pool.cc	(working copy)
@@ -389,7 +389,7 @@
   ConditionVariable has_work_cv_;
 
   // Condition variable that is waited on by non-worker threads (in
-  // FlushForTesting()) until IsIdle() goes to true.
+  // FlushForTesting()) until IsIdle() goes to true or Shutdown completes.
   ConditionVariable is_idle_cv_;
 
   // Condition variable that is waited on by non-worker threads (in
@@ -610,8 +610,9 @@
 }
 
 void SequencedWorkerPool::Inner::FlushForTesting() {
+  base::ThreadRestrictions::ScopedAllowWait allow_wait;
   AutoLock lock(lock_);
-  while (!IsIdle())
+  while (!IsIdle() && !shutdown_called_)
     is_idle_cv_.Wait();
 }
 
@@ -635,8 +636,10 @@
     SignalHasWork();
 
     // There are no pending or running tasks blocking shutdown, we're done.
-    if (CanShutdown())
+    if (CanShutdown()) {
+      is_idle_cv_.Signal();
       return;
+    }
   }
 
   // If we're here, then something is blocking shutdown.  So wait for
@@ -652,6 +655,7 @@
     AutoLock lock(lock_);
     while (!CanShutdown())
       can_shutdown_cv_.Wait();
+    is_idle_cv_.Signal();
   }
   UMA_HISTOGRAM_TIMES("SequencedWorkerPool.ShutdownDelayTime",
                       TimeTicks::Now() - shutdown_wait_begin);