cipd: Make it work on Windows.

go/src/infra/tools/cipd/local/rename_windows.go

Index: go/src/infra/tools/cipd/local/rename_windows.go
diff --git a/go/src/infra/tools/cipd/local/rename_windows.go b/go/src/infra/tools/cipd/local/rename_windows.go
new file mode 100644
index 0000000000000000000000000000000000000000..5c8bb0e64e9fbf729863a9dc09f4a8655d9a6d65
--- /dev/null
+++ b/go/src/infra/tools/cipd/local/rename_windows.go
@@ -0,0 +1,47 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// +build windows
+
+package local
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+// See https://msdn.microsoft.com/en-us/library/windows/desktop/aa365240(v=vs.85).aspx
+
+var (
+	kernel32        = syscall.NewLazyDLL("kernel32.dll")
+	procMoveFileExW = kernel32.NewProc("MoveFileExW")
+)
+
+const (
+	moveFileReplaceExisting = 1
+	moveFileWriteThrough    = 8
+)
+
+func moveFileEx(source, target *uint16, flags uint32) error {
+	ret, _, err := procMoveFileExW.Call(uintptr(unsafe.Pointer(source)), uintptr(unsafe.Pointer(target)), uintptr(flags))
+	if ret == 0 {
+		if err != nil {
+			return err
+		}
+		return syscall.EINVAL
+	}
+	return nil
+}
+
+func atomicRename(source, target string) error {
+	lpReplacedFileName, err := syscall.UTF16PtrFromString(target)
+	if err != nil {
+		return err
+	}
+	lpReplacementFileName, err := syscall.UTF16PtrFromString(source)
+	if err != nil {
+		return err
+	}
+	return moveFileEx(lpReplacementFileName, lpReplacedFileName, moveFileReplaceExisting|moveFileWriteThrough)
+}