Fix concurrent sweeping in predictable mode and bring --concurrent-sweeping flag back.

src/heap/spaces.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/v8.h"
 
 #include "src/base/bits.h"
 #include "src/base/platform/platform.h"
 #include "src/full-codegen.h"
 #include "src/heap/mark-compact.h"
@@ skipping 2551 matching lines @@
   // This counter will be increased for pages which will be swept by the
   // sweeper threads.
   unswept_free_bytes_ = 0;
 
   // Clear the free list before a full GC---it will be rebuilt afterward.
   free_list_.Reset();
 }
 
 
 intptr_t PagedSpace::SizeOfObjects() {
-  DCHECK(FLAG_predictable ||
+  DCHECK(!FLAG_concurrent_sweeping ||
          heap()->mark_compact_collector()->sweeping_in_progress() ||
          (unswept_free_bytes_ == 0));
   return Size() - unswept_free_bytes_ - (limit() - top());
 }
 
 
 // After we have booted, we have created a map which represents free space
 // on the heap.  If there was already a free list then the elements on it
 // were created with the wrong FreeSpaceMap (normally NULL), so we need to
 // fix them.
@@ skipping 583 matching lines @@
     object->ShortPrint();
     PrintF("\n");
   }
   printf(" --------------------------------------\n");
   printf(" Marked: %x, LiveCount: %x\n", mark_size, LiveBytes());
 }
 
 #endif  // DEBUG
 }
 }  // namespace v8::internal