chore: integrate changes required by Theia

Adapts the "menubar" to support documents different than the global
one. This is required when rendering a menubar in a different window
which has its own document.

Adapts the "menu" to remove the check for empty menus. Menus in Theia
are dynamic and therefore by default empty until they are shown. This
check therefore prevents opening all menus in Theia.

packages/widgets/src/menu.ts

@@ -520,7 +520,7 @@ export class Menu extends Widget {
     this.node.addEventListener('mouseenter', this);
     this.node.addEventListener('mouseleave', this);
     this.node.addEventListener('contextmenu', this);
-    document.addEventListener('mousedown', this, true);
+    this.node.ownerDocument.addEventListener('mousedown', this, true);
   }
 
   /**
@@ -533,7 +533,7 @@ export class Menu extends Widget {
     this.node.removeEventListener('mouseenter', this);
     this.node.removeEventListener('mouseleave', this);
     this.node.removeEventListener('contextmenu', this);
-    document.removeEventListener('mousedown', this, true);
+    this.node.ownerDocument.removeEventListener('mousedown', this, true);
   }
 
   /**
@@ -1446,8 +1446,8 @@ namespace Private {
    * Create the DOM node for a menu.
    */
   export function createNode(): HTMLDivElement {
-    let node = document.createElement('div');
-    let content = document.createElement('ul');
+    let node = this.node.ownerDocument.createElement('div');
+    let content = this.node.ownerDocument.createElement('ul');
     content.className = 'lm-Menu-content';
     node.appendChild(content);
     content.setAttribute('role', 'menu');
@@ -1545,8 +1545,8 @@ namespace Private {
     return {
       pageXOffset: window.pageXOffset,
       pageYOffset: window.pageYOffset,
-      clientWidth: document.documentElement.clientWidth,
-      clientHeight: document.documentElement.clientHeight
+      clientWidth: this.node.ownerDocument.documentElement.clientWidth,
+      clientHeight: this.node.ownerDocument.documentElement.clientHeight
     };
   }
 
@@ -1636,7 +1636,7 @@ namespace Private {
     style.maxHeight = `${maxHeight}px`;
 
     // Attach the menu to the document.
-    Widget.attach(submenu, document.body);
+    Widget.attach(submenu, this.node.ownerDocument.body);
 
     // Measure the size of the menu.
     let { width, height } = node.getBoundingClientRect();

packages/widgets/src/menubar.ts

@@ -145,11 +145,6 @@ export class MenuBar extends Widget {
       value = -1;
     }
 
-    // An empty menu cannot be active
-    if (value > -1 && this._menus[value].items.length === 0) {
-      value = -1;
-    }
-
     // Bail early if the index will not change.
     if (this._activeIndex === value) {
       return;