Expose Cache Storage API in global window/worker scope

LayoutTests/http/tests/cachestorage/script-tests/cache-delete.js

-importScripts('worker-testharness.js');
-importScripts('/resources/testharness-helpers.js');
+if (self.importScripts) {
+    importScripts('/resources/testharness.js');
+    importScripts('/resources/testharness-helpers.js');
+    importScripts('../resources/test-helpers.js');
+}
 
 var test_url = 'https://example.com/foo';
 
 // Construct a generic Request object. The URL is |test_url|. All other fields
 // are defaults.
 function new_test_request() {
   return new Request(test_url);
 }
 
 // Construct a generic Response object.
@@ skipping 94 matching lines @@
   cache_test(function(cache) {
       return Promise.all(Object.keys(cache_entries).map(function(k) {
           return cache.put(cache_entries[k].request.clone(),
                            cache_entries[k].response.clone());
         }))
         .then(function() {
             return test_function(cache);
           });
     }, description);
 }
+
+done();