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

pkg/polymer/lib/polymer_element.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.polymer_element;
 
 import 'dart:async';
 import 'dart:html';
 import 'dart:mirrors';
 import 'dart:js' as dartJs;
 
 import 'package:custom_element/custom_element.dart';
 import 'package:js/js.dart' as js;
 import 'package:mdv/mdv.dart' show NodeBinding;
 import 'package:observe/observe.dart';
 import 'package:observe/src/microtask.dart';
 import 'package:polymer_expressions/polymer_expressions.dart';
 
-import 'src/utils_observe.dart' show toCamelCase, toHyphenedName;
+import 'src/utils.dart' show toCamelCase, toHyphenedName;
 
 /**
  * Registers a [PolymerElement]. This is similar to [registerCustomElement]
  * but it is designed to work with the `<element>` element and adds additional
  * features.
  */
 void registerPolymerElement(String localName, PolymerElement create()) {
   registerCustomElement(localName, () => create().._initialize(localName));
 }
 
@@ skipping 525 matching lines @@
   'onKeyMessage': MediaElement.keyMessageEvent,
   'onNeedKey': MediaElement.needKeyEvent,
   'onWebGlContextLost': CanvasElement.webGlContextLostEvent,
   'onWebGlContextRestored': CanvasElement.webGlContextRestoredEvent,
   'onPointerLockChange': Document.pointerLockChangeEvent,
   'onPointerLockError': Document.pointerLockErrorEvent,
   'onReadyStateChange': Document.readyStateChangeEvent,
   'onSelectionChange': Document.selectionChangeEvent,
   'onSecurityPolicyViolation': Document.securityPolicyViolationEvent,
 };