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

runtime/bin/process_linux.cc

Index: runtime/bin/process_linux.cc
diff --git a/runtime/bin/process_linux.cc b/runtime/bin/process_linux.cc
index 184173aa5c4d8740c24bba322132ebd63fe27412..a06556112b2a66fc33b31faa1b9a0b858f0fe829 100644
--- a/runtime/bin/process_linux.cc
+++ b/runtime/bin/process_linux.cc
@@ -551,8 +551,8 @@ 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;
   }