Eliminating some dart2js warnings from polymer_expressions

pkg/polymer_expressions/lib/parser.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.
 
 library polymer_expressions.parser;
 
 import 'tokenizer.dart';
 import 'expression.dart';
 
 const _UNARY_OPERATORS = const ['+', '-', '!'];
@@ skipping 116 matching lines @@
     var kind = _token.kind;
     switch (kind) {
       case KEYWORD_TOKEN:
         var keyword = _token.value;
         if (keyword == 'this') {
           _advance();
           // TODO(justin): return keyword node
           return _astFactory.identifier('this');
         } else if (keyword == 'in') {
           return null;
-        } else {
-          throw new ArgumentError('unrecognized keyword: $keyword');
         }
-        break;
+        throw new ArgumentError('unrecognized keyword: $keyword');
       case IDENTIFIER_TOKEN:
         return _parseInvokeOrIdentifier();
-        break;
       case STRING_TOKEN:
         return _parseString();
-        break;
       case INTEGER_TOKEN:
         return _parseInteger();
-        break;
       case DECIMAL_TOKEN:
         return _parseDecimal();
-        break;
       case GROUPER_TOKEN:
         if (_token.value == '(') {
           return _parseParenthesized();
         } else if (_token.value == '{') {
           return _parseMapLiteral();
         }
         return null;
-        break;
       default:
         return null;
     }
   }
 
   MapLiteral _parseMapLiteral() {
     var entries = [];
     do {
       _advance();
       if (_token.kind == GROUPER_TOKEN && _token.value == '}') {
@@ skipping 102 matching lines @@
     return value;
   }
 
   Literal<double> _parseDecimal([String prefix = '']) {
     var value = _astFactory.literal(double.parse('$prefix${_token.value}'));
     _advance();
     return value;
   }
 
 }