fix #606, allow specifying the summary file extension

test/worker/worker_test.dart

Index: test/worker/worker_test.dart
diff --git a/test/worker/worker_test.dart b/test/worker/worker_test.dart
index 04c5057a7731ca6c4971ab84e5da3f5915f2f5a5..6685acfda3490c08d6723cedb82178cfe5507d9c 100644
--- a/test/worker/worker_test.dart
+++ b/test/worker/worker_test.dart
@@ -101,7 +101,7 @@ main() {
     final helloDart = new File('test/worker/hello.dart').absolute;
 
     final greetingJS = new File('test/worker/greeting.js').absolute;
-    final greetingSummary = new File('test/worker/greeting.sum').absolute;
+    final greetingSummary = new File('test/worker/greeting.api.ds').absolute;
     final helloJS = new File('test/worker/hello_world.js').absolute;
 
     setUp(() {
@@ -122,6 +122,7 @@ main() {
       var result = Process.runSync('dart', [
         'bin/dartdevc.dart',
         'compile',
+        '--summary-extension=api.ds',
         '--no-source-map',
         '-o',
         greetingJS.path,
@@ -138,6 +139,7 @@ main() {
         'compile',
         '--no-source-map',
         '--no-summarize',
+        '--summary-extension=api.ds',
         '-s',
         greetingSummary.path,
         '-o',