Switch polymer's build.dart to use the new linter. This CL does the following

pkg/polymer/lib/src/messages.dart

-// Copyright (c) 2012, 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 messages;
-
-import 'dart:convert';
-
-import 'package:barback/barback.dart' show TransformLogger;
-import 'package:source_maps/span.dart' show Span;
-import 'package:logging/logging.dart' show Level;
-
-import 'compiler_options.dart';
-import 'utils.dart';
-
-/** Map between error levels and their display color. */
-final Map<Level, String> _ERROR_COLORS = (() {
-  var colorsMap = new Map<Level, String>();
-  colorsMap[Level.SEVERE] = RED_COLOR;
-  colorsMap[Level.WARNING] = MAGENTA_COLOR;
-  colorsMap[Level.INFO] = GREEN_COLOR;
-  return colorsMap;
-})();
-
-/** A single message from the compiler. */
-class Message {
-  final Level level;
-  final String message;
-  final Span span;
-  final bool useColors;
-
-  Message(this.level, this.message, {this.span, this.useColors: false});
-
-  String get kind => level == Level.SEVERE ? 'error' :
-      (level == Level.WARNING ? 'warning' : 'info');
-
-  String toString() {
-    var output = new StringBuffer();
-    bool colors = useColors && _ERROR_COLORS.containsKey(level);
-    var levelColor =  _ERROR_COLORS[level];
-    if (colors) output.write(levelColor);
-    output..write(kind)..write(' ');
-    if (colors) output.write(NO_COLOR);
-
-    if (span == null) {
-      output.write(message);
-    } else {
-      output.write(span.getLocationMessage(message, useColors: colors,
-          color: levelColor));
-    }
-
-    return output.toString();
-  }
-
-  String toJson() {
-    if (span == null) return toString();
-    return JSON.encode([{
-      'method': kind,
-      'params': {
-        'file': span.sourceUrl,
-        'message': message,
-        'line': span.start.line + 1,
-        'charStart': span.start.offset,
-        'charEnd': span.end.offset,
-      }
-    }]);
-  }
-}
-
-/**
- * This class tracks and prints information, warnings, and errors emitted by the
- * compiler.
- */
-class Messages implements TransformLogger {
-  final CompilerOptions options;
-  final bool shouldPrint;
-
-  final List<Message> messages = <Message>[];
-
-  Messages({CompilerOptions options, this.shouldPrint: true})
-      : options = options != null ? options : new CompilerOptions();
-
-  /**
-   * Creates a new instance of [Messages] which doesn't write messages to
-   * the console.
-   */
-  Messages.silent(): this(shouldPrint: false);
-
-  /**
-   * True if we have an error that prevents correct codegen.
-   * For example, if we failed to read an input file.
-   */
-  bool get hasErrors => messages.any((m) => m.level == Level.SEVERE);
-
-  // Convenience methods for testing
-  int get length => messages.length;
-
-  Message operator[](int index) => messages[index];
-
-  void clear() {
-    messages.clear();
-  }
-
-  /** [message] is considered a static compile-time error by the Dart lang. */
-  void error(String message, [Span span]) {
-    var msg = new Message(Level.SEVERE, message, span: span,
-        useColors: options.useColors);
-
-    messages.add(msg);
-    printMessage(msg);
-  }
-
-  /** [message] is considered a type warning by the Dart lang. */
-  void warning(String message, [Span span]) {
-    if (options.warningsAsErrors) {
-      error(message, span);
-    } else {
-      var msg = new Message(Level.WARNING, message,
-          span: span, useColors: options.useColors);
-
-      messages.add(msg);
-      printMessage(msg);
-    }
-  }
-
-  /// the list of error messages. Empty list, if there are no error messages.
-  List<Message> get errors =>
-        messages.where((m) => m.level == Level.SEVERE).toList();
-
-  /// the list of warning messages. Empty list if there are no warning messages.
-  List<Message> get warnings =>
-        messages.where((m) => m.level == Level.WARNING).toList();
-
-  /**
-   * [message] at [span] will tell the user about what the compiler
-   * is doing.
-   */
-  void info(String message, [Span span]) {
-    var msg = new Message(Level.INFO, message, span: span,
-        useColors: options.useColors);
-
-    messages.add(msg);
-    if (options.verbose) printMessage(msg);
-  }
-
-  void printMessage(msg) {
-    if (shouldPrint) print(options.jsonFormat ? msg.toJson() : msg);
-  }
-}