Autoselect a port rather than always using 8080 for chrome_test.

test/runner/browser/chrome_test.dart

Index: test/runner/browser/chrome_test.dart
diff --git a/test/runner/browser/chrome_test.dart b/test/runner/browser/chrome_test.dart
index 252211e4de53251b2ea83d7a7ba9df46afe43f71..3d4fd7ceb0663698626eeb5e068609695f99a719 100644
--- a/test/runner/browser/chrome_test.dart
+++ b/test/runner/browser/chrome_test.dart
@@ -117,7 +117,7 @@ webSocket.addEventListener("open", function() {
   });
 
   test("a process can be killed synchronously after it's started", () {
-    return shelf_io.serve(expectAsync((_) {}, count: 0), 'localhost', 8080)
+    return shelf_io.serve(expectAsync((_) {}, count: 0), 'localhost', 0)
         .then((server) {
       var chrome = new Chrome(baseUrlForAddress(server.address, server.port));
       return chrome.close().whenComplete(server.close);