Use the regular start incremental marking strategy in the idle notification.

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 403 matching lines @@
   ActivateIncrementalWriteBarrier(heap_->new_space());
 
   LargePage* lop = heap_->lo_space()->first_page();
   while (lop->is_valid()) {
     SetOldSpacePageFlags(lop, true, is_compacting_);
     lop = lop->next_page();
   }
 }
 
 
+bool IncrementalMarking::ShouldActivate() {
+  return WorthActivating() && heap_->NextGCIsLikelyToBeFull();
+}
+
+
 bool IncrementalMarking::WorthActivating() {
 #ifndef DEBUG
   static const intptr_t kActivationThreshold = 8 * MB;
 #else
   // TODO(gc) consider setting this to some low level so that some
   // debug tests run with incremental marking and some without.
   static const intptr_t kActivationThreshold = 0;
 #endif
   // Only start incremental marking in a safe state: 1) when incremental
   // marking is turned on, 2) when we are currently not in a GC, and
@@ skipping 370 matching lines @@
   if (FLAG_trace_incremental_marking) {
     PrintF("[IncrementalMarking] Complete (normal).\n");
   }
   if (action == GC_VIA_STACK_GUARD) {
     heap_->isolate()->stack_guard()->RequestGC();
   }
 }
 
 
 void IncrementalMarking::OldSpaceStep(intptr_t allocated) {
-  if (IsStopped() && WorthActivating() && heap_->NextGCIsLikelyToBeFull()) {
+  if (IsStopped() && ShouldActivate()) {
     // TODO(hpayer): Let's play safe for now, but compaction should be
     // in principle possible.
     Start(PREVENT_COMPACTION);
   } else {
     Step(allocated * kFastMarking / kInitialMarkingSpeed, GC_VIA_STACK_GUARD);
   }
 }
 
 
 void IncrementalMarking::SpeedUp() {
@@ skipping 143 matching lines @@
   bytes_scanned_ = 0;
   write_barriers_invoked_since_last_step_ = 0;
 }
 
 
 int64_t IncrementalMarking::SpaceLeftInOldSpace() {
   return heap_->MaxOldGenerationSize() - heap_->PromotedSpaceSizeOfObjects();
 }
 }
 }  // namespace v8::internal