Bug 1612738 - Set minimum widget size for mContainer. r=stransky

Differential Revision: https://phabricator.services.mozilla.com/D105514

widget/gtk/mozgtk/mozgtk.c

@@ -480,6 +480,7 @@ STUB(gtk_widget_realize)
 STUB(gtk_widget_reparent)
 STUB(gtk_widget_set_allocation)
 STUB(gtk_widget_set_app_paintable)
+STUB(gtk_widget_set_size_request)
 STUB(gtk_window_set_auto_startup_notification)
 STUB(gtk_window_set_keep_above)
 STUB(gtk_window_set_opacity)

widget/gtk/nsWindow.cpp

@@ -1129,6 +1129,10 @@ void nsWindow::ApplySizeConstraints(void) {
 
     gtk_window_set_geometry_hints(GTK_WINDOW(mShell), nullptr, &geometry,
                                   GdkWindowHints(hints));
+    if (!mIsX11Display) {
+      gtk_widget_set_size_request(GTK_WIDGET(mContainer), geometry.min_width,
+                                  geometry.min_height);
+    }
   }
 }