Correct the sign of exit codes for the process library.

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");
 
 /**
@@ skipping 66 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);
   
-  bool get hasCrashed() => !timedOut && exitCode != 255 && exitCode != 0;
+  bool get hasCrashed() => !timedOut && exitCode != -1 && exitCode != 0;
 
   bool get hasTimedOut() => timedOut;
 
   bool get didFail() => exitCode != 0 && !hasCrashed;
 
   // Reverse result of a negative test.
   bool get hasFailed() => (testCase.isNegative ? !didFail : didFail);
 }
 
 
@@ skipping 84 matching lines @@
       new RunningProcess(test, 60).start();
       numProcesses++;
     }
   }
 
   runTest(TestCase test) {
     tests.add(test);
     tryRunTest();
   }
 }