fix(transform): handle multiple interfaces in directive processor

Comma separate the list of interfaces in the directive transformer.

Closes #2941

modules/angular2/src/transform/directive_processor/rewriter.dart

@@ -193,9 +193,9 @@ class CreateNgDepsVisitor extends Object with SimpleAstVisitor<Object> {
         node.implementsClause.interfaces != null &&
         node.implementsClause.interfaces.isNotEmpty) {
       writer.print(''', 'interfaces': const [''');
-      node.implementsClause.interfaces.forEach((interface) {
-        writer.print('${interface.name}');
-      });
+      writer.print(node.implementsClause.interfaces
+          .map((interface) => interface.name)
+          .join(', '));
       writer.print(']');
     }
     writer.print('})');

modules/angular2/test/transform/directive_processor/interfaces_files/expected/soup.ng_deps.dart

@@ -12,6 +12,6 @@ void initReflector(reflector) {
       'factory': () => new ChangingSoupComponent(),
       'parameters': const [],
       'annotations': const [const Component(selector: '[soup]')],
-      'interfaces': const [OnChange]
+      'interfaces': const [OnChange, AnotherInterface]
     });
 }

modules/angular2/test/transform/directive_processor/interfaces_files/soup.dart

@@ -3,4 +3,4 @@ library dinner.soup;
 import 'package:angular2/src/core/annotations_impl/annotations.dart';
 
 @Component(selector: '[soup]')
-class ChangingSoupComponent implements OnChange {}
+class ChangingSoupComponent implements OnChange, AnotherInterface {}