test.dart: a small fix to handle flakyness with DumpRenderTree and xvfb

tools/testing/dart/test_runner.dart

 // Copyright (c) 2011, 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.
 
 #library("test_runner");
 
 #import("status_file_parser.dart");
 #import("test_progress.dart");
 #import("test_suite.dart");
 
@@ skipping 143 matching lines @@
     if (testCase is !BrowserTestCase) return (exitCode != 0 && !hasCrashed);
 
     // Browser case:
     // Browser tests fail unless stdout contains
     // 'Content-Type: text/plain\nPASS'.
     String previous_line = '';
     for (String line in stdout) {
       if (line == 'PASS' && previous_line == 'Content-Type: text/plain') {
         return (exitCode != 0 && !hasCrashed);
       }
-      // If the browser test failed, it may have been because DumpRenderTree
-      // and the virtual framebuffer X server didn't hook up.
+      previous_line = line;
+    }
+
+    // If the browser test failed, it may have been because DumpRenderTree
+    // and the virtual framebuffer X server didn't hook up.
+    for (String line in stderr) {
       if (line.contains('Gtk-WARNING **: cannot open display: :99')) {
         // If we get the X server error, return the expected value
         // We cannot restart the test from here.  Issue dart:1135 is filed.
         return testCase.isNegative;
       }
-      previous_line = line;
     }
     return true;
   }
 
   // Reverse result of a negative test.
   bool get hasFailed() => (testCase.isNegative ? !didFail : didFail);
 }
 
 
 class RunningProcess {
@@ skipping 319 matching lines @@
           test.displayName != 'dartc/junit_tests') {
         _ensureDartcBatchRunnersStarted(test.executablePath);
         _getDartcBatchRunnerProcess().startTest(test);
       } else {
         new RunningProcess(test).start();
       }
       _numProcesses++;
     }
   }
 }