Group lexical context variables for faster look up.

src/scopes.cc

Index: src/scopes.cc
diff --git a/src/scopes.cc b/src/scopes.cc
index 319aca518ed69187dc29cc817c58f9266b2a8700..ce06976c4c9d2369d208d41ccc53a9431f9cba8e 100644
--- a/src/scopes.cc
+++ b/src/scopes.cc
@@ -593,7 +593,11 @@ class VarAndOrder {
   Variable* var() const { return var_; }
   int order() const { return order_; }
   static int Compare(const VarAndOrder* a, const VarAndOrder* b) {
-    return a->order_ - b->order_;
+    // Sort lexical variables to the end of the list.
+    bool a_is_lexical = IsLexicalVariableMode(a->var()->mode());
+    bool b_is_lexical = IsLexicalVariableMode(b->var()->mode());
+    if (a_is_lexical == b_is_lexical) return a->order_ - b->order_;
+    return a_is_lexical ? 1 : -1;
   }
 
  private: