Allow internal usage of SIGQUIT signal listening.

runtime/bin/process_patch.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.
 
 patch class _WindowsCodePageDecoder {
   /* patch */ static String _decodeBytes(List<int> bytes)
       native "SystemEncodingToString";
 }
 
 
@@ skipping 121 matching lines @@
     if (signal != ProcessSignal.SIGHUP &&
         signal != ProcessSignal.SIGINT &&
         signal != ProcessSignal.SIGTERM &&
         (Platform.isWindows ||
          (signal != ProcessSignal.SIGUSR1 &&
           signal != ProcessSignal.SIGUSR2 &&
           signal != ProcessSignal.SIGWINCH))) {
       throw new SignalException(
           "Listening for signal $signal is not supported");
     }
+    return _watchSignalInternal(signal);
+  }
+
+  static Stream<ProcessSignal> _watchSignalInternal(ProcessSignal signal) {
     if (_signalControllers[signal._signalNumber] == null) {
       _signalControllers[signal._signalNumber] = new _SignalController(signal);
     }
     return _signalControllers[signal._signalNumber].stream;
   }
 }
 
 
 class _ProcessStartStatus {
   int _errorCode;  // Set to OS error code if process start failed.
@@ skipping 398 matching lines @@
   const _ProcessResult(int this.pid,
                        int this.exitCode,
                        this.stdout,
                        this.stderr);
 
   final int pid;
   final int exitCode;
   final stdout;
   final stderr;
 }