Undo change that converted exit code 255 to -1.

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 109 matching lines @@
   TestOutput(this.testCase, this.exitCode, this.timedOut, this.stdout,
              this.stderr, this.time) {
     testCase.output = this;
   }
 
   String get result() =>
       hasCrashed ? CRASH : (hasTimedOut ? TIMEOUT : (hasFailed ? FAIL : PASS));
 
   bool get unexpectedOutput() => !testCase.expectedOutcomes.contains(result);
 
-  // The Java dartc runner exits with code 253 in case of unhandled
-  // exceptions.
-  // The VM uses std::abort to terminate on asserts.
-  // std::abort terminates with exit code 3 on Windows.
   bool get hasCrashed() {
     if (new Platform().operatingSystem() == 'windows') {
+      // The VM uses std::abort to terminate on asserts.
+      // std::abort terminates with exit code 3 on Windows.
       if (exitCode == 3) {
         return !timedOut;
       }
-      return (!timedOut &&
-              (exitCode != -1) &&
-              (exitCode < 0) &&
-              ((0x3FFFFF00 & exitCode) == 0));
+      return (!timedOut && (exitCode < 0) && ((0x3FFFFF00 & exitCode) == 0));
     }
-    return (!timedOut &&
-            (exitCode != -1) &&
-            ((exitCode < 0) || (exitCode == 253)));
+    // The Java dartc runner exits with code 253 in case of unhandled
+    // exceptions.
+    return (!timedOut && ((exitCode < 0) || (exitCode == 253)));
   }
 
   bool get hasTimedOut() => timedOut;
 
   bool get didFail() {
     if (exitCode != 0 && !hasCrashed) return true;
 
     // Browser tests fail unless stdout contains
     // 'Content-Type: text/plain\nPASS'.
     if (testCase is !BrowserTestCase) return false;
@@ skipping 313 matching lines @@
       if (test.configuration['component'] == 'dartc') {
         _ensureDartcBatchRunnersStarted(test.executablePath);
         _getDartcBatchRunnerProcess().startTest(test);
       } else {
         new RunningProcess(test).start();
       }
       _numProcesses++;
     }
   }
 }