os,syscall: implement functions related to uid, gid and pid on js/wasm

This change implements the following functions on js/wasm:
- os.Chown
- os.Fchown
- os.Lchown
- syscall.Getuid
- syscall.Getgid
- syscall.Geteuid
- syscall.Getegid
- syscall.Getgroups
- syscall.Getpid
- syscall.Getppid
- syscall.Umask

Change-Id: Icdb0fafc02c9df6e9e3573542f8499c3464dc671
Reviewed-on: https://go-review.googlesource.com/c/go/+/154157
Run-TryBot: Richard Musiol <neelance@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/syscall/fs_js.go

@@ -244,18 +244,26 @@ func Chown(path string, uid, gid int) error {
 	if err := checkPath(path); err != nil {
 		return err
 	}
-	return ENOSYS
+	_, err := fsCall("chown", path, uint32(uid), uint32(gid))
+	return err
 }
 
 func Fchown(fd int, uid, gid int) error {
-	return ENOSYS
+	_, err := fsCall("fchown", fd, uint32(uid), uint32(gid))
+	return err
 }
 
 func Lchown(path string, uid, gid int) error {
 	if err := checkPath(path); err != nil {
 		return err
 	}
-	return ENOSYS
+	if jsFS.Get("lchown") == js.Undefined() {
+		// fs.lchown is unavailable on Linux until Node.js 10.6.0
+		// TODO(neelance): remove when we require at least this Node.js version
+		return ENOSYS
+	}
+	_, err := fsCall("lchown", path, uint32(uid), uint32(gid))
+	return err
 }
 
 func UtimesNano(path string, ts []Timespec) error {