Run Gallery in editor as well.

Samples/UIWidgetsGallery/GalleryMainEditor.cs

         
         protected override void Awake() {
             base.Awake();
-            FontManager.instance.addFont(Resources.Load<Font>("MaterialIcons-Regular"));
-            FontManager.instance.addFont(Resources.Load<Font>("GalleryIcons"));
+            FontManager.instance.addFont(Resources.Load<Font>("MaterialIcons-Regular"), "Material Icons");
+            FontManager.instance.addFont(Resources.Load<Font>("GalleryIcons"), "GalleryIcons");
         }
     }
 }