Upstream http://cl/362104095

lib/utils/settings.d.ts

@@ -154,4 +154,8 @@ export {setUseAdoptedStyleSheetsWithBuiltCSS};
  */
 declare function setUseAdoptedStyleSheetsWithBuiltCSS(value: boolean): void;
 
+export const useShadow: boolean;
+export const useNativeCSSProperties: boolean;
+export const useNativeCustomElements: boolean;
+export const supportsAdoptingStyleSheets: boolean;
 export let legacyOptimizations: boolean;

polymer-legacy.d.ts

@@ -5,3 +5,5 @@ import {LegacyElementMixin} from './lib/legacy/legacy-element-mixin.js';
 export {Polymer} from './lib/legacy/polymer-fn.js';
 
 export {html} from './lib/utils/html-tag.js';
+
+export const Base: LegacyElementMixin;