[heap] Add a flag guard for concurrent store buffer processing.

src/heap/store-buffer.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/heap/store-buffer.h"
 
 #include <algorithm>
 
 #include "src/counters.h"
 #include "src/heap/incremental-marking.h"
@@ skipping 67 matching lines @@
 }
 
 void StoreBuffer::FlipStoreBuffers() {
   base::LockGuard<base::Mutex> guard(&mutex_);
   int other = (current_ + 1) % kStoreBuffers;
   MoveEntriesToRememberedSet(other);
   lazy_top_[current_] = top_;
   current_ = other;
   top_ = start_[current_];
 
-  if (!task_running_) {
+  if (!task_running_ && FLAG_concurrent_sweeping) {
     task_running_ = true;
     Task* task = new Task(heap_->isolate(), this);
     V8::GetCurrentPlatform()->CallOnBackgroundThread(
         task, v8::Platform::kShortRunningTask);
   }
 }
 
 void StoreBuffer::MoveEntriesToRememberedSet(int index) {
   if (!lazy_top_[index]) return;
   DCHECK_GE(index, 0);
@@ skipping 43 matching lines @@
     StoreBufferOverflow(heap_->isolate());
   }
   *top_ = MarkDeletionAddress(start);
   top_++;
   *top_ = end;
   top_++;
 }
 
 }  // namespace internal
 }  // namespace v8