Declare the sequence of phases for the full polymer transform and add tests for

pkg/polymer/lib/src/transform/code_extractor.dart

Index: pkg/polymer/lib/src/transform/code_extractor.dart
diff --git a/pkg/polymer/lib/src/transform/code_extractor.dart b/pkg/polymer/lib/src/transform/code_extractor.dart
index 5f7058f01974f4dc335fbe5a05e797e577f45925..61fd2c6db382f73453d9d45a123f38e84a99bc83 100644
--- a/pkg/polymer/lib/src/transform/code_extractor.dart
+++ b/pkg/polymer/lib/src/transform/code_extractor.dart
@@ -26,18 +26,28 @@ class InlineCodeExtractor extends Transformer {
       var document = parseHtml(content, inputId.path, transform.logger);
       int count = 0;
       for (var tag in document.queryAll('script')) {
-        if (tag.attributes['type'] == 'application/dart' &&
-            !tag.attributes.containsKey('src')) {
-          // TODO(sigmund): should we automatically include a library directive
-          // if it doesn't have one?
-          var filename = path.url.basename(inputId.path);
-          tag.attributes['src'] = '$filename.$count.dart';
-          var textContent = tag.nodes.first;
-          var id = inputId.addExtension('.$count.dart');
-          transform.addOutput(new Asset.fromString(id, textContent.value));
-          textContent.remove();
+        // Only process tags that have inline Dart code
+        if (tag.attributes['type'] != 'application/dart' ||
+          tag.attributes.containsKey('src')) {
+          continue;
+        }
+
+        // Remove empty tags
+        if (tag.nodes.length == 0) {
+          tag.remove();
           count++;

[Jennifer Messerly, 2013/08/23 01:23:11]

instead of count, a boolean "htmlChanged" might be more clear.

[Siggi Cherem (dart-lang), 2013/08/23 01:45:28]

Done.

+          continue;
         }
+
+        // TODO(sigmund): should we automatically include a library directive
+        // if it doesn't have one?
+        var filename = path.url.basename(inputId.path);
+        tag.attributes['src'] = '$filename.$count.dart';

[Jennifer Messerly, 2013/08/23 01:23:11]

I forgot the outcome of previous CL discussion, should we have a TODO here to
ensure this filename is unique?

[Siggi Cherem (dart-lang), 2013/08/23 01:45:28]

Added TODO. Yeah, we weren't sure how necessary it is to worry about it right
away, so meanwhile  I opened this bug for barback:
https://code.google.com/p/dart/issues/detail?id=12618

+        var textContent = tag.nodes.first;
+        var id = inputId.addExtension('.$count.dart');
+        transform.addOutput(new Asset.fromString(id, textContent.value));
+        textContent.remove();
+        count++;
       }
       transform.addOutput(new Asset.fromString(inputId,
           count == 0 ? content : document.outerHtml));