[parser,ast] Simplify MarkExpressionAsAssigned.

src/ast/ast.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_AST_AST_H_
 #define V8_AST_AST_H_
 
 #include "src/ast/ast-types.h"
 #include "src/ast/ast-value-factory.h"
 #include "src/ast/modules.h"
@@ skipping 1644 matching lines @@
   void set_var(Variable* v) {
     DCHECK(!is_resolved());
     DCHECK_NOT_NULL(v);
     var_ = v;
   }
 
   bool is_this() const { return IsThisField::decode(bit_field_); }
 
   bool is_assigned() const { return IsAssignedField::decode(bit_field_); }
   void set_is_assigned() {
+    DCHECK(!is_resolved());
     bit_field_ = IsAssignedField::update(bit_field_, true);
   }
 
   bool is_resolved() const { return IsResolvedField::decode(bit_field_); }
   void set_is_resolved() {
     bit_field_ = IsResolvedField::update(bit_field_, true);
   }
 
   bool is_new_target() const { return IsNewTargetField::decode(bit_field_); }
   void set_is_new_target() {
@@ skipping 1927 matching lines @@
                                     : NULL;                                   \
   }
 AST_NODE_LIST(DECLARE_NODE_FUNCTIONS)
 #undef DECLARE_NODE_FUNCTIONS
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_AST_AST_H_