Give Process.kill an optional argument to specify which signal to send.

runtime/bin/process.h

 // 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.
 
 #ifndef BIN_PROCESS_H_
 #define BIN_PROCESS_H_
 
 #include "bin/builtin.h"
 #include "platform/globals.h"
 
@@ skipping 10 matching lines @@
                    intptr_t environment_length,
                    intptr_t* in,
                    intptr_t* out,
                    intptr_t* err,
                    intptr_t* id,
                    intptr_t* exit_handler,
                    char* os_error_message,
                    int os_error_message_len);
 
   // Kill a process with a given pid.
-  static bool Kill(intptr_t id);
+  static bool Kill(intptr_t id, int signal);
 
   // Terminate the exit code handler thread. Does not return before
   // the thread has terminated.
   static void TerminateExitCodeHandler();
 
   DISALLOW_ALLOCATION();
   DISALLOW_IMPLICIT_CONSTRUCTORS(Process);
 };
 
 #endif  // BIN_PROCESS_H_