ART: Change ThreadPool::Wait behavior

When a pool is in the stopped state, Wait() will not wait for all
tasks to complete.

Bug: 31385354
Test: m test-art-host-gtest-thread_pool_test
Change-Id: Id0144b685ee2fddf1a1c2c2ca334251130121033
diff --git a/runtime/thread_pool.cc b/runtime/thread_pool.cc
index b14f340..65fd999 100644
--- a/runtime/thread_pool.cc
+++ b/runtime/thread_pool.cc
@@ -177,7 +177,7 @@
     }
 
     ++waiting_count_;
-    if (waiting_count_ == GetThreadCount() && tasks_.empty()) {
+    if (waiting_count_ == GetThreadCount() && !HasOutstandingTasks()) {
       // We may be done, lets broadcast to the completion condition.
       completion_condition_.Broadcast(self);
     }
@@ -200,7 +200,7 @@
 }
 
 Task* ThreadPool::TryGetTaskLocked() {
-  if (started_ && !tasks_.empty()) {
+  if (HasOutstandingTasks()) {
     Task* task = tasks_.front();
     tasks_.pop_front();
     return task;
@@ -218,7 +218,7 @@
   }
   // Wait until each thread is waiting and the task list is empty.
   MutexLock mu(self, task_queue_lock_);
-  while (!shutting_down_ && (waiting_count_ != GetThreadCount() || !tasks_.empty())) {
+  while (!shutting_down_ && (waiting_count_ != GetThreadCount() || HasOutstandingTasks())) {
     if (!may_hold_locks) {
       completion_condition_.Wait(self);
     } else {