vpython: Add primary execution package.

vpython/system_windows.go

Index: vpython/system_windows.go
diff --git a/vpython/system_windows.go b/vpython/system_windows.go
new file mode 100644
index 0000000000000000000000000000000000000000..f25b5781ed494068f62788af58bcb0aece10a99f
--- /dev/null
+++ b/vpython/system_windows.go
@@ -0,0 +1,18 @@
+// Copyright 2017 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+package vpython
+
+import (
+	"os"
+	"syscall"
+)
+
+// forwardedSignals is the list of signals that should be forwarded to the
+// Python subproess.
+var forwardedSignals = []os.Signal{
+	syscall.SIGHUP,
+	syscall.SIGINT,
+	syscall.SIGQUIT,
+}