Use idle task to perform incremental marking steps.

src/heap/incremental-marking.cc

Index: src/heap/incremental-marking.cc
diff --git a/src/heap/incremental-marking.cc b/src/heap/incremental-marking.cc
index b420cb728c0a401c5c4a93187ddce12b6cc42c38..4fe9eef3456d7f87079eef6b9773ce3ca926d1b4 100644
--- a/src/heap/incremental-marking.cc
+++ b/src/heap/incremental-marking.cc
@@ -11,6 +11,7 @@
 #include "src/heap/mark-compact-inl.h"
 #include "src/heap/objects-visiting.h"
 #include "src/heap/objects-visiting-inl.h"
+#include "src/v8.h"
 
 namespace v8 {
 namespace internal {
@@ -486,6 +487,7 @@ void IncrementalMarking::Start(const char* reason) {
   }
 
   heap_->new_space()->LowerInlineAllocationLimit(kAllocatedThreshold);
+  incremental_marking_job()->Start(heap_);
 }