Expose Cache Storage API in global window/worker scope

Source/modules/serviceworkers/WorkerCacheStorage.idl

Index: Source/modules/serviceworkers/WorkerCacheStorage.idl
diff --git a/Source/modules/serviceworkers/WorkerCacheStorage.idl b/Source/modules/serviceworkers/WorkerCacheStorage.idl
new file mode 100644
index 0000000000000000000000000000000000000000..eb60fe48501e22fa140bc06043ce4c84b2481290
--- /dev/null
+++ b/Source/modules/serviceworkers/WorkerCacheStorage.idl
@@ -0,0 +1,11 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// https://slightlyoff.github.io/ServiceWorker/spec/service_worker/#self-caches
+[
+    RuntimeEnabled=GlobalCacheStorage,
+    ImplementedAs=GlobalCacheStorage,
+] partial interface WorkerGlobalScope {
+  [CallWith=ScriptState, Unforgeable, MeasureAs=GlobalCacheStorage, RuntimeEnabled=GlobalCacheStorage, RaisesException] readonly attribute CacheStorage caches;
+};