shellEntry: Support lockdown of "Show Text" menu in password entries

Some deployments require being able to prevent users from showing
the password they're currently typing.

This commit adds support for that kind of lockdown.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/687

js/ui/shellEntry.js

@@ -1,17 +1,24 @@
 // -*- mode: js; js-indent-level: 4; indent-tabs-mode: nil -*-
 /* exported addContextMenu CapsLockWarning */
 
-const { Clutter, GObject, Pango, Shell, St } = imports.gi;
+const { Clutter, Gio, GObject, Pango, Shell, St } = imports.gi;
 
 const BoxPointer = imports.ui.boxpointer;
 const Main = imports.ui.main;
 const Params = imports.misc.params;
 const PopupMenu = imports.ui.popupMenu;
 
+const LOCKDOWN_SCHEMA = 'org.gnome.desktop.lockdown';
+const DISABLE_SHOW_PASSWORD_KEY = 'disable-show-password';
+
 var EntryMenu = class extends PopupMenu.PopupMenu {
     constructor(entry) {
         super(entry, 0, St.Side.TOP);
 
+        this._lockdownSettings = new Gio.Settings({ schema_id: LOCKDOWN_SCHEMA });
+        this._lockdownSettings.connect(`changed::${DISABLE_SHOW_PASSWORD_KEY}`,
+            this._applyLockdownSettings.bind(this));
+
         this._entry = entry;
         this._clipboard = St.Clipboard.get_default();
 
@@ -39,6 +46,20 @@ var EntryMenu = class extends PopupMenu.PopupMenu {
         item.connect('activate', this._onPasswordActivated.bind(this));
         this.addMenuItem(item);
         this._passwordItem = item;
+        this._applyLockdownSettings();
+    }
+
+    _applyLockdownSettings() {
+        if (!this._passwordItem)
+            return;
+
+        let passwordDisabled = this._lockdownSettings.get_boolean(DISABLE_SHOW_PASSWORD_KEY);
+
+        this._passwordItem.visible = !passwordDisabled;
+        this._entry.show_peek_icon = !passwordDisabled;
+
+        if (passwordDisabled)
+            this._entry.password_visible = false;
     }
 
     open(animate) {