[heap] Properly handle --noconcurrent-sweeping flag in page unmapper.

BUG=

Review-Url: https://codereview.chromium.org/2347073003
Cr-Commit-Position: refs/heads/master@{#39544}

src/heap/incremental-marking.cc

@@ -1163,8 +1163,8 @@ void IncrementalMarking::SpeedUp() {
 void IncrementalMarking::FinalizeSweeping() {
   DCHECK(state_ == SWEEPING);
   if (heap_->mark_compact_collector()->sweeping_in_progress() &&
-      (heap_->mark_compact_collector()->sweeper().IsSweepingCompleted() ||
-       !FLAG_concurrent_sweeping)) {
+      (!FLAG_concurrent_sweeping ||
+       heap_->mark_compact_collector()->sweeper().IsSweepingCompleted())) {
     heap_->mark_compact_collector()->EnsureSweepingCompleted();
   }
   if (!heap_->mark_compact_collector()->sweeping_in_progress()) {

src/heap/mark-compact.cc

@@ -567,6 +567,7 @@ void MarkCompactCollector::EnsureSweepingCompleted() {
 }
 
 bool MarkCompactCollector::Sweeper::IsSweepingCompleted() {
+  DCHECK(FLAG_concurrent_sweeping);
   while (pending_sweeper_tasks_semaphore_.WaitFor(
       base::TimeDelta::FromSeconds(0))) {
     num_sweeping_tasks_.Increment(-1);

src/heap/spaces.cc

@@ -398,7 +398,7 @@ bool MemoryAllocator::CanFreeMemoryChunk(MemoryChunk* chunk) {
   // We cannot free memory chunks in new space while the sweeper is running
   // since a sweeper thread might be stuck right before trying to lock the
   // corresponding page.
-  return !chunk->InNewSpace() || (mc == nullptr) ||
+  return !chunk->InNewSpace() || (mc == nullptr) || !FLAG_concurrent_sweeping ||
          mc->sweeper().IsSweepingCompleted();
 }