Turn Scope::locals_ into a ThreadedList

src/crankshaft/typing.cc

Index: src/crankshaft/typing.cc
diff --git a/src/crankshaft/typing.cc b/src/crankshaft/typing.cc
index 579fc394730219a7445d40628f358c65eac404b1..f21d235cb3c3f3a4234315e659b7eaa774841ac7 100644
--- a/src/crankshaft/typing.cc
+++ b/src/crankshaft/typing.cc
@@ -85,10 +85,8 @@ void AstTyper::ObserveTypesAtOsrEntry(IterationStatement* stmt) {
                     store_.LookupBounds(parameter_index(i)).lower);
     }
 
-    ZoneList<Variable*>* local_vars = scope_->locals();
     int local_index = 0;
-    for (int i = 0; i < local_vars->length(); i++) {
-      Variable* var = local_vars->at(i);
+    for (Variable* var : *scope_->locals()) {
       if (var->IsStackLocal()) {
         PrintObserved(
             var, frame->GetExpression(local_index),