vpython: Add VirtualEnv creation package.

vpython/venv/system_windows.go

Index: vpython/venv/system_windows.go
diff --git a/vpython/venv/system_windows.go b/vpython/venv/system_windows.go
new file mode 100644
index 0000000000000000000000000000000000000000..e4e7121fce0233f9443de41fdbcabff19603758a
--- /dev/null
+++ b/vpython/venv/system_windows.go
@@ -0,0 +1,36 @@
+// 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 venv
+
+import (
+	"os"
+	"path/filepath"
+	"syscall"
+
+	"github.com/luci/luci-go/common/errors"
+)
+
+// longestGeneratedScriptPath returns the path of the longest generated script
+// given a VirtualEnv root.
+//
+// Since Windows doesn't generate scripts, this is disabled.
+func longestGeneratedScriptPath(basedir string) string { return "" }
+
+// venvBinPath resolves the path to a VirtualEnv binary.
+func venvBinPath(root, name string) string {
+	return filepath.Join(root, "Scripts", name)
+}
+
+func checkProcessRunning(pid int) error {
+	proc, err := os.FindProcess(pid)
+	if err != nil {
+		return errors.Annotate(err).Reason("failed to find process").Err()
+	}
+
+	if err := proc.Signal(os.Signal(syscall.Signal(0))); err != nil {
+		return errors.Annotate(err).Reason("failed to signal process").Err()
+	}
+	return nil
+}