First step towards asynchronous loading of sources

tests/standalone/http_launch_test.dart

 // Copyright (c) 2013, 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.
 // VMOptions=
 // VMOptions=--short_socket_read
 // VMOptions=--short_socket_write
 // VMOptions=--short_socket_read --short_socket_write
 //
 // Test:
 //   *) Launching a script fetched over HTTP.
@@ skipping 56 matching lines @@
     // Check results.
     checkResults(results);
   });
 }
 
 checkResults(List<ProcessResult> results) {
   Expect.equals(4, results.length);
   // Exited cleanly.
   for (int i = 0; i < results.length; i++) {
     ProcessResult result = results[i];
+    if (result.exitCode != 0) {
+      print("Exit code for process $i = ${result.exitCode}");
+      print("---stdout:---\n${result.stdout}");
+      print("---stderr:---\n${result.stderr}\n---");
+    }
     Expect.equals(0, result.exitCode);
   }
   String stdout = results[0].stdout;
   // Output is the string 'hello'. Use startsWith to avoid new line differences.
+  if (!stdout.startsWith('hello')) {
+    print("---- stdout of remote process:\n$stdout\n----");
+  }
   Expect.isTrue(stdout.startsWith('hello'));
   // Same output from all three process runs.
   for (int i = 0; i < results.length; i++) {
     Expect.equals(stdout, results[i].stdout);
   }
 }
 
 main() {
   HttpServer.bind(InternetAddress.LOOPBACK_IP_V4, 0).then(serverRunning);
 }