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

runtime/bin/process_win.cc

 // 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.
 
 #include <process.h>
 
 #include "bin/builtin.h"
 #include "bin/process.h"
 #include "bin/eventhandler.h"
 #include "bin/thread.h"
@@ skipping 493 matching lines @@
 
 bool Process::Kill(intptr_t id, int signal) {
   USE(signal);  // signal is not used on windows.
   HANDLE process_handle;
   HANDLE wait_handle;
   HANDLE exit_pipe;
   bool success = ProcessInfoList::LookupProcess(id,
                                                 &process_handle,
                                                 &wait_handle,
                                                 &exit_pipe);
-  if (!success) {
-    return true;  // The process has already died.  Report a successful kill.
-  }
+  // The process is already dead.
+  if (!success) return false;
   BOOL result = TerminateProcess(process_handle, -1);
   return result ? true : false;
 }
 
 
 void Process::TerminateExitCodeHandler() {
   // Nothing needs to be done on Windows.
 }
 
 
 intptr_t Process::CurrentProcessId() {
   return static_cast<intptr_t>(GetCurrentProcessId());
 }