Use const for const/final top-levels, types, symbols.

lib/src/js/builder.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // Utilities for building JS ASTs at runtime.  Contains a builder class
 // and a parser that parses part of the language.
 
 part of js_ast;
 
 
@@ skipping 1158 matching lines @@
     declare(firstVariable);
     while (acceptCategory(COMMA)) {
       String variable = lastToken;
       expectCategory(ALPHA);
       declare(variable);
     }
     return new VariableDeclarationList(keyword, initialization);
   }
 
   Expression parseVarDeclarationOrExpression() {
-    var keyword = acceptVarOrLet();
+    var keyword = acceptVarLetOrConst();
     if (keyword != null) {
       return parseVariableDeclarationList(keyword);
     } else {
       return parseExpression();
     }
   }
 
   /** Accepts a `var` or `let` keyword. If neither is found, returns null. */
-  String acceptVarOrLet() {
+  String acceptVarLetOrConst() {
     if (acceptString('var')) return 'var';
     if (acceptString('let')) return 'let';
+    if (acceptString('const')) return 'const';
     return null;
   }
 
   Expression expression() {
     Expression expression = parseVarDeclarationOrExpression();
     if (lastCategory != NONE || position != src.length) {
       error("Unparsed junk: ${categoryToString(lastCategory)}");
     }
     return expression;
   }
@@ skipping 38 matching lines @@
       if (acceptString('if')) return parseIfThenElse();
 
       if (acceptString('for')) return parseFor();
 
       if (acceptString('function')) return parseFunctionDeclaration();
 
       if (acceptString('class')) return new ClassDeclaration(parseClass());
 
       if (acceptString('try')) return parseTry();
 
-      var keyword = acceptVarOrLet();
+      var keyword = acceptVarLetOrConst();
       if (keyword != null) {
         Expression declarations = parseVariableDeclarationList(keyword);
         expectSemicolon();
         return new ExpressionStatement(declarations);
       }
 
       if (acceptString('while')) return parseWhile();
 
       if (acceptString('do')) return parseDo();
 
@@ skipping 105 matching lines @@
       }
       Statement body = parseStatement();
       return new For(init, condition, update, body);
     }
 
     expectCategory(LPAREN);
     if (acceptCategory(SEMICOLON)) {
       return finishFor(null);
     }
 
-    var keyword = acceptVarOrLet();
+    var keyword = acceptVarLetOrConst();
     if (keyword != null) {
       String identifier = lastToken;
       expectCategory(ALPHA);
 
       if (acceptString('in')) {
         Expression objectExpression = parseExpression();
         expectCategory(RPAREN);
         Statement body = parseStatement();
         return new ForIn(
             _createVariableDeclarationList(keyword, identifier),
@@ skipping 197 matching lines @@
       expectCategory(RSQUARE);
       return expr;
     } else if (acceptCategory(HASH)) {
       return parseInterpolatedExpression();
     } else {
       error('Expected property name');
       return null;
     }
   }
 }