Function registerContext

test/angular/1.7/angular.js:9206–9208

(ctx, values)

   */
  (function registerNativePropertyContexts() {
    function registerContext(ctx, values) {
      forEach(values, function(v) { PROP_CONTEXTS[v.toLowerCase()] = ctx; });
    }

    registerContext(SCE_CONTEXTS.HTML, [
      'iframe|srcdoc',