Clean up some messiness in Scopes.

src/ast.h

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 930 matching lines @@
   VariableProxy* value() const { return value_; }
 
  private:
   Literal* key_;
   VariableProxy* value_;
 };
 
 
 class VariableProxy: public Expression {
  public:
+  explicit VariableProxy(Variable* var);
+
   virtual void Accept(AstVisitor* v);
 
   // Type testing & conversion
   virtual Property* AsProperty() {
     return var_ == NULL ? NULL : var_->AsProperty();
   }
 
   virtual VariableProxy* AsVariableProxy() {
     return this;
   }
 
   Variable* AsVariable() {
-    return this == NULL || var_ == NULL ? NULL : var_->AsVariable();
+    if (this == NULL || var_ == NULL) return NULL;
+    Expression* rewrite = var_->rewrite();
+    if (rewrite == NULL || rewrite->AsSlot() != NULL) return var_;
+    return NULL;
   }
 
   virtual bool IsValidLeftHandSide() {
     return var_ == NULL ? true : var_->IsValidLeftHandSide();
   }
 
   virtual bool IsTrivial() {
     // Reading from a mutable variable is a side effect, but the
     // variable for 'this' is immutable.
     return is_this_ || is_trivial_;
@@ skipping 940 matching lines @@
   AST_NODE_LIST(DEF_VISIT)
 #undef DEF_VISIT
 
  private:
   bool stack_overflow_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_AST_H_