Fetch: Make Headers' constructor match the current spec IDL.

third_party/WebKit/Source/modules/fetch/ResponseInit.idl

Index: third_party/WebKit/Source/modules/fetch/ResponseInit.idl
diff --git a/third_party/WebKit/Source/modules/fetch/ResponseInit.idl b/third_party/WebKit/Source/modules/fetch/ResponseInit.idl
index 6829802068a7a627b5ffaac10c3ab2e617da4269..8dc8e0d5a7946d25aa54a75bb9d6fe29aa03f557 100644
--- a/third_party/WebKit/Source/modules/fetch/ResponseInit.idl
+++ b/third_party/WebKit/Source/modules/fetch/ResponseInit.idl
@@ -4,14 +4,6 @@
 
 // https://fetch.spec.whatwg.org/#responseinit
 
-// The actual typedef in the spec is
-//    (sequence<sequence<ByteString>> or record<ByteString,ByteString>)
-// which also implicitly includes Headers since it is iterable.
-// Blink's WebIDL code does not support record<K,V> yet, so we have to make do
-// with the (Dictionary or Headers) part instead.
-// See http://crbug.com/685754.
-typedef (sequence<sequence<ByteString>> or Dictionary or Headers) HeadersInit;
-
 dictionary ResponseInit {
     unsigned short status = 200;
     ByteString statusText = "OK";