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

runtime/bin/process_macos.cc

Index: runtime/bin/process_macos.cc
diff --git a/runtime/bin/process_macos.cc b/runtime/bin/process_macos.cc
index f71b461dd36a3bd240ca84d310e9223c33cf1293..f152b07475d9c17e4fc633d96b970a03c0c9ab2e 100644
--- a/runtime/bin/process_macos.cc
+++ b/runtime/bin/process_macos.cc
@@ -550,8 +550,8 @@ int Process::Start(const char* path,
 }
 
 
-bool Process::Kill(intptr_t id) {
-  int result = TEMP_FAILURE_RETRY(kill(id, SIGKILL));
+bool Process::Kill(intptr_t id, int signal) {
+  int result = TEMP_FAILURE_RETRY(kill(id, signal));
   if (result == -1) {
     return false;
   }