IDL: Support iterable<>, maplike<> and setlike<> syntax

Source/modules/fetch/Headers.idl

Index: Source/modules/fetch/Headers.idl
diff --git a/Source/modules/fetch/Headers.idl b/Source/modules/fetch/Headers.idl
index dad4fcc7a4ae82959b9dce22310ffc287de0b98a..39e09c947acce046274878244fa804a7958ff4d8 100644
--- a/Source/modules/fetch/Headers.idl
+++ b/Source/modules/fetch/Headers.idl
@@ -9,7 +9,6 @@ typedef Dictionary OpenEndedDictionary;
     Constructor(Headers input),
     Constructor(OpenEndedDictionary input),
     Constructor(sequence<sequence<ByteString>> input),
-    Iterable,
     Exposed(Window GlobalFetch, DedicatedWorker GlobalFetch, SharedWorker GlobalFetch, ServiceWorker ServiceWorker),
     RaisesException=Constructor,
     GarbageCollected,
@@ -21,4 +20,5 @@ typedef Dictionary OpenEndedDictionary;
     [RaisesException] sequence<ByteString> getAll(ByteString name);
     [RaisesException] boolean has(ByteString key);
     [RaisesException] void set(ByteString key, ByteString value);
+    iterable<ByteString, ByteString>;
 };