Fix idle step marking after 9d7ebc.

Idle notification should force marking to make progress.

BUG=

Review URL: https://codereview.chromium.org/1275573002

Cr-Commit-Position: refs/heads/master@{#30041}

src/heap/heap.cc

@@ -4859,7 +4859,7 @@ bool Heap::PerformIdleTimeAction(GCIdleTimeAction action,
     case DO_INCREMENTAL_MARKING: {
       const double remaining_idle_time_in_ms =
           AdvanceIncrementalMarking(action.parameter, deadline_in_ms,
-                                    IncrementalMarking::NoForcedStepActions());
+                                    IncrementalMarking::IdleStepActions());
       if (remaining_idle_time_in_ms > 0.0) {
         action.additional_work = TryFinalizeIdleIncrementalMarking(
             remaining_idle_time_in_ms, heap_state.size_of_objects,

src/heap/incremental-marking.cc

@@ -16,9 +16,9 @@ namespace v8 {
 namespace internal {
 
 
-IncrementalMarking::StepActions IncrementalMarking::NoForcedStepActions() {
+IncrementalMarking::StepActions IncrementalMarking::IdleStepActions() {
   return StepActions(IncrementalMarking::NO_GC_VIA_STACK_GUARD,
-                     IncrementalMarking::DO_NOT_FORCE_MARKING,
+                     IncrementalMarking::FORCE_MARKING,
                      IncrementalMarking::DO_NOT_FORCE_COMPLETION);
 }
 

src/heap/incremental-marking.h

@@ -39,7 +39,7 @@ class IncrementalMarking {
     ForceCompletionAction force_completion;
   };
 
-  static StepActions NoForcedStepActions();
+  static StepActions IdleStepActions();
 
   explicit IncrementalMarking(Heap* heap);