Expose Cache Storage API in global window/worker scope

LayoutTests/resources/testharness-helpers.js

 /*
  * testharness-helpers contains various useful extensions to testharness.js to
  * allow them to be used across multiple tests before they have been
  * upstreamed. This file is intended to be usable from both document and worker
  * environments, so code should for example not rely on the DOM.
  */
 
 // Returns a promise that fulfills after the provided |promise| is fulfilled.
 // The |test| succeeds only if |promise| rejects with an exception matching
 // |code|. Accepted values for |code| follow those accepted for assert_throws().
@@ skipping 143 matching lines @@
         if (typeof src != "object")
             return src;
         var dst = Array.isArray(src) ? [] : {};
         for (var property in src) {
             dst[property] = deepCopy(src[property]);
         }
         return dst;
     }
     return JSON.stringify(deepCopy(object));
 }