Expose Cache Storage API in global window/worker scope

LayoutTests/http/tests/cachestorage/script-tests/cache-storage.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');
+}
 
 promise_test(function(t) {
     var cache_name = 'cache-storage/foo';
     return self.caches.delete(cache_name)
       .then(function() {
           return self.caches.open(cache_name);
         })
       .then(function(cache) {
           assert_true(cache instanceof Cache,
                       'CacheStorage.open should return a Cache.');
@@ skipping 165 matching lines @@
       .then(function(cache_exists) {
           assert_true(cache_exists,
                       'CacheStorage names should be not be converted.');
         })
       .then(function() { return self.caches.has(converted_name); })
       .then(function(cache_exists) {
           assert_false(cache_exists,
                        'CacheStorage names should be not be converted.');
         });
   }, 'CacheStorage names are DOMStrings not USVStrings');
+
+done();