Fix race between VisitSmiRoots and SetStackLimit.

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index 66b527456e6ec53b1f149b378576a08b59b614a9..4855ac08aeb8e1a56b23df4e527edd97208e977e 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -6161,6 +6161,8 @@ void Heap::IterateWeakRoots(ObjectVisitor* v, VisitMode mode) {
 
 
 void Heap::IterateSmiRoots(ObjectVisitor* v) {
+  // Acquire execution access since we are going to read stack limit values.
+  ExecutionAccess access(isolate());
   v->VisitPointers(&roots_[kSmiRootsStart], &roots_[kRootListLength]);
   v->Synchronize(VisitorSynchronization::kSmiRootList);
 }