Updating code_transformer's ResolverTransform to filter on Dart entry points in apply.

pkg/code_transformers/lib/src/entry_point.dart

 // Copyright (c) 2014, 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.
 import 'dart:async';
 
 import 'package:analyzer/analyzer.dart' as analyzer;
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:barback/barback.dart';
 
-/// Checks to see if the provided Asset is a Dart entry point.
+/// Checks to see if the provided AssetId is a Dart file in a directory which
+/// may contain entry points.
 ///
-/// Assets are considered entry points if they are Dart files located in
-/// web/, test/, benchmark/ or example/ and have a main() function.
+/// Directories are considered entry points if they are Dart files located in
+/// web/, test/, benchmark/ or example/.
+bool isPossibleDartEntryId(AssetId id) {
+  if (id.extension != '.dart') return false;
+
+  return ['benchmark', 'example', 'test', 'web']
+      .any((dir) => id.path.startsWith("$dir/"));
+}
+
+/// Checks to see if the provided Asset is possibly a Dart entry point.
+///
+/// Assets are considered entry points if they pass [isPossibleDartEntryId] and
+/// have a main() method.
 ///
 /// Because this only analyzes the primary asset this may return true for files
 /// which are not dart entries if the file does not have a main() but does have
 /// parts or exports.
 Future<bool> isPossibleDartEntry(Asset asset) {
-  if (asset.id.extension != '.dart') return new Future.value(false);
+  if (!isPossibleDartEntryId(asset.id)) return new Future.value(false);
 
-  if (!['benchmark', 'example', 'test', 'web']
-      .any((dir) => asset.id.path.startsWith("$dir/"))) {
-    return new Future.value(false);
-  }
   return asset.readAsString().then((contents) {
     return _couldBeEntrypoint(
         analyzer.parseCompilationUnit(contents, suppressErrors: true));
   });
 }
 
 bool _couldBeEntrypoint(CompilationUnit compilationUnit) {
   // Allow two or fewer arguments so that entrypoints intended for use with
   // [spawnUri] get counted.
   var hasMain = compilationUnit.declarations.any((node) =>
       node is FunctionDeclaration &&
       node.name.name == "main" &&
       node.functionExpression.parameters.parameters.length <= 2);
 
   if (hasMain) return true;
 
   // If it has an export or a part, assume the worst- that the main could be
   // in there.
   // We avoid loading those since this can be run from isPrimaryAsset calls
   // where we do not have access to other sources.
   return compilationUnit.directives.any((node) =>
       node is ExportDirective || node is PartDirective);
 }