Change Process.kill to return a boolean instead of throwing an exception when kill fails.

runtime/bin/process_impl.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.
 
 _exit(int status) native "Exit";
 
 class _ProcessStartStatus {
   int _errorCode;  // Set to OS error code if process start failed.
   String _errorMessage;  // Set to OS error message if process start failed.
 }
@@ skipping 210 matching lines @@
     return _err.inputStream;
   }
 
   OutputStream get stdin {
     if (_closed) {
       throw new ProcessException("Process closed");
     }
     return _out.outputStream;
   }
 
-  void kill([ProcessSignal signal = ProcessSignal.SIGTERM]) {
+  bool kill([ProcessSignal signal = ProcessSignal.SIGTERM]) {
     if (signal is! ProcessSignal) {
       throw new ArgumentError(
           "Argument 'signal' must be a ProcessSignal");
     }
     assert(_started);
-    if (_ended) return;
-    if (_kill(this, signal._signalNumber)) return;
-    throw new ProcessException("Could not kill process");
+    if (_ended) return false;
+    return _kill(this, signal._signalNumber);
   }
 
   bool _kill(Process p, int signal) native "Process_Kill";
 
   void close() {
     if (_closed) {
       throw new ProcessException("Process closed");
     }
     _in.close();
     _out.close();
@@ skipping 122 matching lines @@
 
 class _ProcessResult implements ProcessResult {
   const _ProcessResult(int this.exitCode,
                        String this.stdout,
                        String this.stderr);
 
   final int exitCode;
   final String stdout;
   final String stderr;
 }