Use idle task to perform incremental marking steps.

src/heap/incremental-marking.h

Index: src/heap/incremental-marking.h
diff --git a/src/heap/incremental-marking.h b/src/heap/incremental-marking.h
index 18c8c0dbb20011e3d427da1e827cfdb6089e397c..e0b449a124022f767848e0aa753c6c0f8b701aa3 100644
--- a/src/heap/incremental-marking.h
+++ b/src/heap/incremental-marking.h
@@ -5,14 +5,15 @@
 #ifndef V8_HEAP_INCREMENTAL_MARKING_H_
 #define V8_HEAP_INCREMENTAL_MARKING_H_
 
+#include "src/cancelable-task.h"
 #include "src/execution.h"
+#include "src/heap/incremental-marking-job.h"
 #include "src/heap/mark-compact.h"
 #include "src/objects.h"
 
 namespace v8 {
 namespace internal {
 
-
 class IncrementalMarking {
  public:
   enum State { STOPPED, SWEEPING, MARKING, COMPLETE };
@@ -197,6 +198,10 @@ class IncrementalMarking {
 
   Heap* heap() const { return heap_; }
 
+  IncrementalMarkingJob* incremental_marking_job() {
+    return &incremental_marking_job_;
+  }
+
  private:
   int64_t SpaceLeftInOldSpace();
 
@@ -255,6 +260,8 @@ class IncrementalMarking {
 
   GCRequestType request_type_;
 
+  IncrementalMarkingJob incremental_marking_job_;
+
   DISALLOW_IMPLICIT_CONSTRUCTORS(IncrementalMarking);
 };
 }