Roll 50: Copied IDLs, PYTHON scripts from WebKit removed deleted files in WebCore

core/streams/UnderlyingSourceBase.idl

Index: core/streams/UnderlyingSourceBase.idl
diff --git a/core/streams/UnderlyingSourceBase.idl b/core/streams/UnderlyingSourceBase.idl
new file mode 100644
index 0000000000000000000000000000000000000000..0c0486fddbfea1ceca07201d99870e01d88598e2
--- /dev/null
+++ b/core/streams/UnderlyingSourceBase.idl
@@ -0,0 +1,15 @@
+// Copyright 2016 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.
+
+// This is not a spec interface. Instead, it is used to generate bindings
+// so that Blink code which wishes to create a stream can derive from
+// UnderlyingSourceBase, and a JavaScript object can then be generated
+// automatically for use in initializing a ReadableStream.
+
+[NoInterfaceObject, GarbageCollected, DependentLifetime]
+interface UnderlyingSourceBase {
+    [CallWith=ScriptState, ImplementedAs=startWrapper] Promise<void> start(any stream);
+    [CallWith=ScriptState] Promise<void> pull();
+    [CallWith=ScriptState, ImplementedAs=cancelWrapper] Promise<void> cancel([Default=Undefined] optional any reason);
+};