[heap] Use a separate concurrent store buffer processing flag.

BUG=chromium:697049

Review-Url: https://codereview.chromium.org/2723473002
Cr-Commit-Position: refs/heads/master@{#43492}

src/flag-definitions.h

@@ -650,6 +650,8 @@ DEFINE_INT(max_incremental_marking_finalization_rounds, 3,
 DEFINE_BOOL(minor_mc, false, "perform young generation mark compact GCs")
 DEFINE_NEG_IMPLICATION(minor_mc, incremental_marking)
 DEFINE_BOOL(black_allocation, true, "use black allocation")
+DEFINE_BOOL(concurrent_store_buffer, true,
+            "use concurrent store buffer processing")
 DEFINE_BOOL(concurrent_sweeping, true, "use concurrent sweeping")
 DEFINE_BOOL(parallel_compaction, true, "use parallel compaction")
 DEFINE_BOOL(parallel_pointer_update, true,
@@ -1251,7 +1253,7 @@ DEFINE_BOOL(single_threaded, false, "disable the use of background tasks")
 DEFINE_NEG_IMPLICATION(single_threaded, concurrent_recompilation)
 DEFINE_NEG_IMPLICATION(single_threaded, concurrent_sweeping)
 DEFINE_NEG_IMPLICATION(single_threaded, parallel_compaction)
-
+DEFINE_NEG_IMPLICATION(single_threaded, concurrent_store_buffer)
 
 #undef FLAG
 

src/heap/store-buffer.cc

@@ -91,7 +91,7 @@ void StoreBuffer::FlipStoreBuffers() {
   current_ = other;
   top_ = start_[current_];
 
-  if (!task_running_ && FLAG_concurrent_sweeping) {
+  if (!task_running_ && FLAG_concurrent_store_buffer) {
     task_running_ = true;
     Task* task = new Task(heap_->isolate(), this);
     V8::GetCurrentPlatform()->CallOnBackgroundThread(