Avoid incremental marking write-barrier when constructing descriptor arrays.

src/incremental-marking.h

Index: src/incremental-marking.h
diff --git a/src/incremental-marking.h b/src/incremental-marking.h
index 8457a14cf895351d7f477fcc8618cf71f4ada4a7..fa7337b78fd5ae822ae787b8f09d00478d530f5e 100644
--- a/src/incremental-marking.h
+++ b/src/incremental-marking.h
@@ -198,6 +198,14 @@ class IncrementalMarking {
     }
   }
 
+  void EnterNoMarkingScope() {
+    no_marking_scope_depth_++;
+  }
+
+  void LeaveNoMarkingScope() {
+    no_marking_scope_depth_--;
+  }
+
  private:
   void set_should_hurry(bool val) {
     should_hurry_ = val;
@@ -249,6 +257,8 @@ class IncrementalMarking {
   int allocation_marking_factor_;
   intptr_t allocated_;
 
+  int no_marking_scope_depth_;
+
   DISALLOW_IMPLICIT_CONSTRUCTORS(IncrementalMarking);
 };