Revert "Revert "modalDialog: Destroy dialogs on close""

This reverts commit 007820b7c1.

(I only meant to revert that in my local branch)

js/ui/modalDialog.js

@@ -38,13 +38,15 @@ const ModalDialog = new Lang.Class({
                                         styleClass: null,
                                         parentActor: Main.uiGroup,
                                         keybindingMode: Shell.KeyBindingMode.SYSTEM_MODAL,
-                                        shouldFadeIn: true });
+                                        shouldFadeIn: true,
+                                        destroyOnClose: true });
 
         this.state = State.CLOSED;
         this._hasModal = false;
         this._keybindingMode = params.keybindingMode;
         this._shellReactive = params.shellReactive;
         this._shouldFadeIn = params.shouldFadeIn;
+        this._destroyOnClose = params.destroyOnClose;
 
         this._group = new St.Widget({ visible: false,
                                       x: 0,
@@ -277,6 +279,9 @@ const ModalDialog = new Lang.Class({
                                    this.state = State.CLOSED;
                                    this._group.hide();
                                    this.emit('closed');
+
+                                   if (this._destroyOnClose)
+                                       this.destroy();
                                })
                          });
     },