Perform smaller marking steps incrementally in idle notification.

BUG=

Review URL: https://codereview.chromium.org/767233003

Cr-Commit-Position: refs/heads/master@{#25607}

src/heap/gc-idle-time-handler.cc

@@ -27,7 +27,8 @@ void GCIdleTimeAction::Print() {
       PrintF("no action");
       break;
     case DO_INCREMENTAL_MARKING:
-      PrintF("incremental marking with step %" V8_PTR_PREFIX "d", parameter);
+      PrintF("incremental marking with step %" V8_PTR_PREFIX "d / ms",
+             parameter);
       break;
     case DO_SCAVENGE:
       PrintF("scavenge");
@@ -250,7 +251,7 @@ GCIdleTimeAction GCIdleTimeHandler::Compute(double idle_time_in_ms,
     return GCIdleTimeAction::Nothing();
   }
   size_t step_size = EstimateMarkingStepSize(
-      static_cast<size_t>(idle_time_in_ms),
+      static_cast<size_t>(kIncrementalMarkingStepTimeInMs),
       heap_state.incremental_marking_speed_in_bytes_per_ms);
   return GCIdleTimeAction::IncrementalMarking(step_size);
 }

src/heap/gc-idle-time-handler.h

@@ -125,6 +125,9 @@ class GCIdleTimeHandler {
   // If contexts are disposed at a higher rate a full gc is triggered.
   static const double kHighContextDisposalRate;
 
+  // Incremental marking step time.
+  static const size_t kIncrementalMarkingStepTimeInMs = 1;
+
   class HeapState {
    public:
     void Print();

src/heap/heap.cc

@@ -4489,12 +4489,18 @@ bool Heap::IdleNotification(double deadline_in_seconds) {
       if (incremental_marking()->IsStopped()) {
         incremental_marking()->Start();
       }
-      incremental_marking()->Step(action.parameter,
-                                  IncrementalMarking::NO_GC_VIA_STACK_GUARD,
-                                  IncrementalMarking::FORCE_MARKING,
-                                  IncrementalMarking::DO_NOT_FORCE_COMPLETION);
-      double remaining_idle_time_in_ms =
-          deadline_in_ms - MonotonicallyIncreasingTimeInMs();
+      double remaining_idle_time_in_ms = 0.0;
+      do {
+        incremental_marking()->Step(
+            action.parameter, IncrementalMarking::NO_GC_VIA_STACK_GUARD,
+            IncrementalMarking::FORCE_MARKING,
+            IncrementalMarking::DO_NOT_FORCE_COMPLETION);
+        remaining_idle_time_in_ms =
+            deadline_in_ms - MonotonicallyIncreasingTimeInMs();
+      } while (remaining_idle_time_in_ms >=
+                   2.0 * GCIdleTimeHandler::kIncrementalMarkingStepTimeInMs &&
+               !incremental_marking()->IsComplete() &&
+               !mark_compact_collector_.marking_deque()->IsEmpty());
       if (remaining_idle_time_in_ms > 0.0) {
         TryFinalizeIdleIncrementalMarking(
             remaining_idle_time_in_ms, heap_state.size_of_objects,