[compiler] Improve let+const decision in AstNumbering.

src/ast/ast-numbering.cc

Index: src/ast/ast-numbering.cc
diff --git a/src/ast/ast-numbering.cc b/src/ast/ast-numbering.cc
index a8e63c0018741bb07b44bc505c4920562e200514..f84321de4c84f17c96f8dd309b07f821c87109a7 100644
--- a/src/ast/ast-numbering.cc
+++ b/src/ast/ast-numbering.cc
@@ -161,7 +161,10 @@ void AstNumberingVisitor::VisitVariableProxyReference(VariableProxy* node) {
     default:
       break;
   }
-  if (IsLexicalVariableMode(node->var()->mode())) {
+  if (node->var()->binding_needs_init()) {
+    // Disable FCG+CS for all variable bindings that need explicit
+    // initialization, i.e. ES2015 style const and let, but not
+    // named function expressions.
     DisableFullCodegenAndCrankshaft(kReferenceToLetOrConstVariable);
   }
   node->set_base_id(ReserveIdRange(VariableProxy::num_ids()));