Methods that need browser-specific implementations for Hyperlink. By default, we're very conservative and let the browser handle any clicks with non-left buttons or with modifier keys. This happens to be the correct behavior for Firefox.

class HyperlinkImpl {

 /**
  * Default version, useful for Firefox. Don't fire if it's a rightclick,
  * middleclick, or if any modifiers are held down.
  */
 bool handleAsClick(dart_html.MouseEvent event) {
   int mouseButtons = event.button;
   bool alt = event.altKey;
   bool ctrl = event.ctrlKey;
   bool meta = event.metaKey;
   bool shift = event.shiftKey;
   bool modifiers = alt || ctrl || meta || shift;
   bool middle = mouseButtons == 1;
   bool right = mouseButtons == 2;

   return !modifiers && !middle && !right;
 }
}