Move common features to new WindowOrWorkerGlobalScope mix-in

third_party/WebKit/Source/core/frame/WindowOrWorkerGlobalScope.idl

Index: third_party/WebKit/Source/core/frame/WindowOrWorkerGlobalScope.idl
diff --git a/third_party/WebKit/Source/core/frame/WindowOrWorkerGlobalScope.idl b/third_party/WebKit/Source/core/frame/WindowOrWorkerGlobalScope.idl
new file mode 100644
index 0000000000000000000000000000000000000000..07a12aa849e40737ab2f85bb54a7422eb975c574
--- /dev/null
+++ b/third_party/WebKit/Source/core/frame/WindowOrWorkerGlobalScope.idl
@@ -0,0 +1,13 @@
+// Copyright 2017 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://html.spec.whatwg.org/multipage/webappapis.html#windoworworkerglobalscope-mixin
+
+[
+    NoInterfaceObject, // Always used on target of 'implements'
+    Exposed=(Window,Worker),
+] interface WindowOrWorkerGlobalScope {
+    [RaisesException] DOMString btoa(DOMString btoa);
+    [RaisesException] DOMString atob(DOMString atob);
+};