fix duplicate script issue

pkg/polymer/lib/src/mirror_loader.dart

Index: pkg/polymer/lib/src/mirror_loader.dart
diff --git a/pkg/polymer/lib/src/mirror_loader.dart b/pkg/polymer/lib/src/mirror_loader.dart
index c0cea5c46aa11a15844976eb30e895880f332fe0..257d4e2e6902629f22a13dff4d8de7e05621c102 100644
--- a/pkg/polymer/lib/src/mirror_loader.dart
+++ b/pkg/polymer/lib/src/mirror_loader.dart
@@ -65,7 +65,8 @@ List<Function> discoverInitializers(Iterable<String> librariesToLoad) {
 /// called after all HTML imports are resolved. Polymer ensures this by asking
 /// users to put their Dart script tags after all HTML imports (this is checked
 /// by the linter, and Dartium will otherwise show an error message).
-List<_ScriptInfo> _discoverScripts(Document doc, String baseUri, [_State state]) {
+List<_ScriptInfo> _discoverScripts(
+    Document doc, String baseUri, [_State state]) {
   if (state == null) state = new _State();
   if (doc == null) {
     print('warning: $baseUri not found.');
@@ -77,7 +78,13 @@ List<_ScriptInfo> _discoverScripts(Document doc, String baseUri, [_State state])
     if (node is LinkElement) {
       _discoverScripts(node.import, node.href, state);
     } else if (node is ScriptElement && node.type == 'application/dart') {
-      state.scripts.add(_scriptInfoFor(node, baseUri));
+      var info = _scriptInfoFor(node, baseUri);
+      // Bail and warn if this script has already been seen.
+      if (state.scripts.any((s) => s.resolvedUrl == info.resolvedUrl)) {

[Siggi Cherem (dart-lang), 2014/10/21 17:06:03]

similarly here, let's avoid the linear lookup. One option would be to add a Set
in _State for urls that we have already loaded, or make `scripts` a
LinkedHashMap, where the key is the resolvedUrl.

[jakemac, 2014/10/21 18:14:01]

Done.

+        print('warning: script `${info.resolvedUrl}` included more than once.');

[Siggi Cherem (dart-lang), 2014/10/21 17:06:03]

consider including the short link to the details here.

[jakemac, 2014/10/21 18:14:01]

Done.

+        continue;
+      };
+      state.scripts.add(info);
     }
   }
   return state.scripts;