[heap] Do not wait for marking deque uncommit task on tear down.

Cancelable task already guarantees proper waiting.

BUG=

Review-Url: https://codereview.chromium.org/2462553002
Cr-Commit-Position: refs/heads/master@{#40647}

src/heap/mark-compact.cc

@@ -2119,7 +2119,6 @@ void MarkingDeque::SetUp() {
 }
 
 void MarkingDeque::TearDown() {
-  CancelOrWaitForUncommitTask();
   delete backing_store_;
 }
 
@@ -2187,26 +2186,13 @@ void MarkingDeque::EnsureCommitted() {
 
 void MarkingDeque::StartUncommitTask() {
   if (!uncommit_task_pending_) {
-    UncommitTask* task = new UncommitTask(heap_->isolate(), this);
-    uncommit_task_id_ = task->id();
     uncommit_task_pending_ = true;
+    UncommitTask* task = new UncommitTask(heap_->isolate(), this);
     V8::GetCurrentPlatform()->CallOnBackgroundThread(
         task, v8::Platform::kShortRunningTask);
   }
 }
 
-void MarkingDeque::CancelOrWaitForUncommitTask() {
-  base::LockGuard<base::Mutex> guard(&mutex_);
-  if (!uncommit_task_pending_ ||
-      heap_->isolate()->cancelable_task_manager()->TryAbort(
-          uncommit_task_id_) != CancelableTaskManager::kTaskRunning) {
-    return;
-  }
-  while (uncommit_task_pending_) {
-    uncommit_task_barrier_.Wait(&mutex_);
-  }
-}
-
 class MarkCompactCollector::ObjectStatsVisitor
     : public MarkCompactCollector::HeapObjectVisitor {
  public:

src/heap/mark-compact.h

@@ -64,7 +64,6 @@ class MarkingDeque {
         overflowed_(false),
         in_use_(false),
         uncommit_task_pending_(false),
-        uncommit_task_id_(0),
         heap_(heap) {}
 
   void SetUp();
@@ -144,7 +143,6 @@ class MarkingDeque {
         marking_deque_->Uncommit();
       }
       marking_deque_->uncommit_task_pending_ = false;
-      marking_deque_->uncommit_task_barrier_.NotifyOne();
     }
 
     MarkingDeque* marking_deque_;
@@ -163,10 +161,7 @@ class MarkingDeque {
   // Must be called with mutex lock.
   void StartUncommitTask();
 
-  void CancelOrWaitForUncommitTask();
-
   base::Mutex mutex_;
-  base::ConditionVariable uncommit_task_barrier_;
 
   base::VirtualMemory* backing_store_;
   size_t backing_store_committed_size_;
@@ -182,7 +177,6 @@ class MarkingDeque {
   // committed and will stay committed at least until in_use_ == false.
   bool in_use_;
   bool uncommit_task_pending_;
-  uint32_t uncommit_task_id_;
   Heap* heap_;
 
   DISALLOW_COPY_AND_ASSIGN(MarkingDeque);

test/cctest/heap/test-mark-compact.cc

@@ -69,6 +69,7 @@ TEST(MarkingDeque) {
 
   CHECK_EQ(original_address, current_address);
   s.StopUsing();
+  CcTest::i_isolate()->cancelable_task_manager()->CancelAndWait();
   s.TearDown();
 }