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

src/heap/mark-compact.cc

 // Copyright 2012 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/mark-compact.h"
 
 #include "src/base/atomicops.h"
 #include "src/base/bits.h"
 #include "src/base/sys-info.h"
 #include "src/code-stubs.h"
@@ skipping 549 matching lines @@
   heap()->map_space()->RefillFreeList();
 
 #ifdef VERIFY_HEAP
   if (FLAG_verify_heap && !evacuation()) {
     VerifyEvacuation(heap_);
   }
 #endif
 }
 
 bool MarkCompactCollector::Sweeper::IsSweepingCompleted() {
+  DCHECK(FLAG_concurrent_sweeping);
   while (pending_sweeper_tasks_semaphore_.WaitFor(
       base::TimeDelta::FromSeconds(0))) {
     num_sweeping_tasks_.Increment(-1);
   }
   return num_sweeping_tasks_.Value() == 0;
 }
 
 const char* AllocationSpaceName(AllocationSpace space) {
   switch (space) {
     case NEW_SPACE:
@@ skipping 3461 matching lines @@
       // The target is always in old space, we don't have to record the slot in
       // the old-to-new remembered set.
       DCHECK(!heap()->InNewSpace(target));
       RecordRelocSlot(host, &rinfo, target);
     }
   }
 }
 
 }  // namespace internal
 }  // namespace v8