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

Source/modules/fetch/Headers.h

Index: Source/modules/fetch/Headers.h
diff --git a/Source/modules/fetch/Headers.h b/Source/modules/fetch/Headers.h
index e7a1d93ae2fce8970dc6bbe0dfb7c517619d60d0..bd100544b2b6dd81eb897e91c6bf99455a0db9a5 100644
--- a/Source/modules/fetch/Headers.h
+++ b/Source/modules/fetch/Headers.h
@@ -42,7 +42,7 @@ public:
     bool has(const String& key, ExceptionState&);
     void set(const String& key, const String& value, ExceptionState&);
 
-    // Iterable
+    // iterable<ByteString, ByteString>
     Iterator* iterator(ScriptState*, ExceptionState&);
 
     void setGuard(Guard guard) { m_guard = guard; }