Make progress in incremental marking if scavenge is delaying mark-sweep.

src/spaces.cc

Index: src/spaces.cc
diff --git a/src/spaces.cc b/src/spaces.cc
index a404b1e75ee5cc6537753aae7716e8c2fbd57b23..6144464304898fdb3fe814cceeadc87f5e48881d 100644
--- a/src/spaces.cc
+++ b/src/spaces.cc
@@ -1234,13 +1234,15 @@ MaybeObject* NewSpace::SlowAllocateRaw(int size_in_bytes) {
         allocation_info_.limit + inline_allocation_limit_step_,
         high);
     int bytes_allocated = static_cast<int>(new_top - top_on_previous_step_);
-    heap()->incremental_marking()->Step(bytes_allocated);
+    heap()->incremental_marking()->Step(
+        bytes_allocated, IncrementalMarking::GC_VIA_STACK_GUARD);
     top_on_previous_step_ = new_top;
     return AllocateRaw(size_in_bytes);
   } else if (AddFreshPage()) {
     // Switched to new page. Try allocating again.
     int bytes_allocated = static_cast<int>(old_top - top_on_previous_step_);
-    heap()->incremental_marking()->Step(bytes_allocated);
+    heap()->incremental_marking()->Step(
+        bytes_allocated, IncrementalMarking::GC_VIA_STACK_GUARD);
     top_on_previous_step_ = to_space_.page_low();
     return AllocateRaw(size_in_bytes);
   } else {