[ServiceWorker] CacheStorage tests.

LayoutTests/http/tests/serviceworker/resources/worker-test-harness.js

Index: LayoutTests/http/tests/serviceworker/resources/worker-test-harness.js
diff --git a/LayoutTests/http/tests/serviceworker/resources/worker-test-harness.js b/LayoutTests/http/tests/serviceworker/resources/worker-test-harness.js
index 1d3a5f576840015fc44df81b7e357ab7c5e76b51..3d45c2270cce1988908fb58366f3f7d07a2635aa 100644
--- a/LayoutTests/http/tests/serviceworker/resources/worker-test-harness.js
+++ b/LayoutTests/http/tests/serviceworker/resources/worker-test-harness.js
@@ -84,3 +84,21 @@ function promise_test(func, name, properties) {
         throw value;
       }));
 }
+
+// Returns a promise that fulfills after the provided |promise| is fulfilled.
+// The |test| succeeds only if |promise| throws a DOM exception matching |code|.
+// The optional |description| describes the test being performed.
+// E.g.:
+//   assert_promise_throws(
+//       new Promise(...), // something that should throw an exception.
+//       'NotFoundError',
+//       'Should throw NotFoundError.');
+function assert_promise_throws(promise, code, description) {
+  return promise.then(
+    function() {
+      throw 'assert_promise_throws: ' + description + ' Promise did now throw.';
+    },
+    function(e) {
+      assert_throws(code, function() { throw e; }, description);
+    });
+}