script compactor now names its bootstrap file based off the html entrypoint, not the dart file

lib/build/script_compactor.dart

 // Copyright (c) 2015, 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 web_components.build.script_compactor;
 
 import 'dart:async';
 import 'package:analyzer/analyzer.dart';
 import 'package:barback/barback.dart';
 import 'package:code_transformers/assets.dart';
 import 'package:code_transformers/messages/build_logger.dart';
@@ skipping 86 matching lines @@
 
         // Create the new bootstrap file and return its AssetId.
         return _buildBootstrapFile(mainScript, importScripts);
       });
     });
   }
 
   /// Builds the bootstrap file and returns the path to it relative to
   /// [primaryInput].
   Asset _buildBootstrapFile(AssetId mainScript, Set<AssetId> importScripts) {
-    var bootstrapId = new AssetId(mainScript.package,
-        mainScript.path.replaceFirst('.dart', '.bootstrap.dart'));
+    var bootstrapId = new AssetId(primaryInput.package,
+        primaryInput.path.replaceFirst('.html', '.bootstrap.dart'));
 
     var buffer = new StringBuffer();
     buffer.writeln('library ${_libraryNameFor(bootstrapId)};');
     buffer.writeln();
     var i = 0;
     for (var script in importScripts) {
       var path = _importPath(script, primaryInput);
       buffer.writeln("import '$path' as i$i;");
       i++;
     }
@@ skipping 133 matching lines @@
   if (parts[0] == 'lib') {
     parts[0] = id.package;
     return 'package:${path.url.joinAll(parts)}';
   }
   return path.url.relative(id.path, from: path.url.dirname(primaryInput.path));
 }
 
 // Constant and final variables
 final _invalidLibCharsRegex = new RegExp('[^a-z0-9_]');
 final _numRegex = new RegExp('[0-9]');