Check that script tag has at least src or inlined text, add unrelated test

pkg/polymer/lib/src/build/linter.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.
 
 /// Logic to validate that developers are correctly using Polymer constructs.
 /// This is mainly used to produce warnings for feedback in the editor.
 library polymer.src.build.linter;
 
 import 'dart:async';
 
@@ skipping 269 matching lines @@
     var src = node.attributes['src'];
 
     if (isDart) {
       if (_dartTagSeen) _logger.warning(ONLY_ONE_TAG, span: node.sourceSpan);
       if (_isEntrypoint && _polymerExperimentalHtmlSeen) {
         _logger.warning(NO_DART_SCRIPT_AND_EXPERIMENTAL, span: node.sourceSpan);
       }
       _dartTagSeen = true;
     }
 
-    if (src == null) return;
+    var isEmpty = node.innerHtml.trim() == '';
+
+    if (src == null) {
+      if (isDart && isEmpty) {
+        _logger.warning('script tag seems empty.', span: node.sourceSpan);
+      }
+      return;
+    }
 
     if (src.endsWith('.dart') && !isDart) {
       _logger.warning('Wrong script type, expected type="application/dart".',
           span: node.sourceSpan);
       return;
     }
 
     if (!src.endsWith('.dart') && isDart) {
       _logger.warning('"application/dart" scripts should use the .dart file '
           'extension.', span: node.sourceSpan);
       return;
     }
 
-    if (node.innerHtml.trim() != '') {
+    if (!isEmpty) {
       _logger.warning('script tag has "src" attribute and also has script '
           'text.', span: node.sourceSpan);
     }
   }
 
   /// Produces warnings for misuses of on-foo event handlers, and for instanting
   /// custom tags incorrectly.
   void _validateNormalElement(Element node) {
     // Event handlers only allowed inside polymer-elements
     node.attributes.forEach((name, value) {
@@ skipping 122 matching lines @@
 const String USE_INIT_DART =
     'To run a polymer application, you need to call "initPolymer". You can '
     'either include a generic script tag that does this for you:'
     '\'<script type="application/dart">export "package:polymer/init.dart";'
     '</script>\' or add your own script tag and call that function. '
     'Make sure the script tag is placed after all HTML imports.';
 
 const String NO_DART_SCRIPT_AND_EXPERIMENTAL =
     'The experimental bootstrap feature doesn\'t support script tags on '
     'the main document (for now).';