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

src/heap/incremental-marking.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/v8.h"
 
 #include "src/heap/incremental-marking.h"
 
 #include "src/code-stubs.h"
 #include "src/compilation-cache.h"
@@ skipping 918 matching lines @@
     intptr_t bytes_to_process =
         marking_speed_ *
         Max(allocated_, write_barriers_invoked_since_last_step_);
     allocated_ = 0;
     write_barriers_invoked_since_last_step_ = 0;
 
     bytes_scanned_ += bytes_to_process;
 
     if (state_ == SWEEPING) {
       if (heap_->mark_compact_collector()->sweeping_in_progress() &&
-          heap_->mark_compact_collector()->IsSweepingCompleted()) {
+          (heap_->mark_compact_collector()->IsSweepingCompleted() ||
+           !FLAG_concurrent_sweeping)) {
         heap_->mark_compact_collector()->EnsureSweepingCompleted();
       }
       if (!heap_->mark_compact_collector()->sweeping_in_progress()) {
         bytes_scanned_ = 0;
         StartMarking(PREVENT_COMPACTION);
       }
     } else if (state_ == MARKING) {
       bytes_processed = ProcessMarkingDeque(bytes_to_process);
       if (marking_deque_.IsEmpty()) {
         if (completion == FORCE_COMPLETION ||
@@ skipping 48 matching lines @@
 void IncrementalMarking::IncrementIdleMarkingDelayCounter() {
   idle_marking_delay_counter_++;
 }
 
 
 void IncrementalMarking::ClearIdleMarkingDelayCounter() {
   idle_marking_delay_counter_ = 0;
 }
 }
 }  // namespace v8::internal