Created a bug for the 'cannot open display' issue and made it independend of display number

tools/testing/dart/test_runner.dart

 // Copyright (c) 2012, 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.
 
 /**
  * Classes and methods for executing tests.
  *
  * This module includes:
  * - Managing parallel execution of tests, including timeout checks.
  * - Evaluating the output of each test as pass/fail/crash/timeout.
@@ skipping 606 matching lines @@
   }
 
   bool get _failedBecauseOfMissingXDisplay {
     // Browser case:
     // If the browser test failed, it may have been because DumpRenderTree
     // and the virtual framebuffer X server didn't hook up, or DRT crashed with
     // a core dump. Sometimes DRT crashes after it has set the stdout to PASS,
     // so we have to do this check first.
     var stderrLines = new String.fromCharCodes(super.stderr).split("\n");
     for (String line in stderrLines) {
-      if (line.contains('Gtk-WARNING **: cannot open display: :99') ||
+      // TODO(kustermann,ricow): Issue: 7564
+      // This seems to happen quite frequently, we need to figure out why.
+      if (line.contains('Gtk-WARNING **: cannot open display') ||
           line.contains('Failed to run command. return code=1')) {
         // If we get the X server error, or DRT crashes with a core dump, retry
         // the test.
         if ((testCase as BrowserTestCase).numRetries > 0) {
           requestRetry = true;
         }
         print("Warning: Test failure because of missing XDisplay");
         return true;
       }
     }
@@ skipping 1098 matching lines @@
         // the developer doesn't waste his or her time trying to fix a bunch of
         // tests that appear to be broken but were actually just flakes that
         // didn't get retried because there had already been one failure.
         bool allowRetry = _MAX_FAILED_NO_RETRY > _progress.numFailedTests;
         new RunningProcess(test, allowRetry, this).start();
       }
       _numProcesses++;
     }
   }
 }