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

runtime/bin/process_win.cc

Index: runtime/bin/process_win.cc
diff --git a/runtime/bin/process_win.cc b/runtime/bin/process_win.cc
index 07df45420eb0a0c8445dedefd402427f78a583fe..b24cf8937c6f5b22cef0bb5ae428c75bfa11aa67 100644
--- a/runtime/bin/process_win.cc
+++ b/runtime/bin/process_win.cc
@@ -500,7 +500,8 @@ int Process::Start(const char* path,
 }
 
 
-bool Process::Kill(intptr_t id) {
+bool Process::Kill(intptr_t id, int signal) {
+  // signal is not used on windows.
   HANDLE process_handle;
   HANDLE wait_handle;
   HANDLE exit_pipe;