cocoa: Enable modifying initialized menu

atom/browser/ui/cocoa/atom_menu_controller.h

@@ -39,6 +39,9 @@ class MenuModel;
 // to the contents of the model after calling this will not be noticed.
 - (id)initWithModel:(ui::MenuModel*)model;
 
+// Populate current NSMenu with |model|.
+- (void)populateWithModel:(ui::MenuModel*)model;
+
 // Programmatically close the constructed menu.
 - (void)cancel;
 

atom/browser/ui/cocoa/atom_menu_controller.mm

@@ -93,6 +93,22 @@ int EventFlagsFromNSEvent(NSEvent* event) {
   [super dealloc];
 }
 
+- (void)populateWithModel:(ui::MenuModel*)model {
+  if (!menu_)
+    return;
+
+  model_ = model;
+  [menu_ removeAllItems];
+
+  const int count = model->GetItemCount();
+  for (int index = 0; index < count; index++) {
+    if (model->GetTypeAt(index) == ui::MenuModel::TYPE_SEPARATOR)
+      [self addSeparatorToMenu:menu_ atIndex:index];
+    else
+      [self addItemToMenu:menu_ atIndex:index fromModel:model];
+  }
+}
+
 - (void)cancel {
   if (isMenuOpen_) {
     [menu_ cancelTracking];