LibWeb: Implement operation to error a ReadableStream

Author: https://github.com/trflynn89
Commit: https://github.com/SerenityOS/serenity/commit/88d46b51ed
Pull-request: https://github.com/SerenityOS/serenity/pull/24452
Issue: https://github.com/SerenityOS/serenity/issues/23847

Userland/Libraries/LibWeb/Streams/ReadableStream.cpp

@@ -186,6 +186,22 @@ void ReadableStream::close()
         });
 }
 
+// https://streams.spec.whatwg.org/#readablestream-error
+void ReadableStream::error(JS::Value error)
+{
+    controller()->visit(
+        // 1. If stream.[[controller]] implements ReadableByteStreamController, then perform
+        //    ! ReadableByteStreamControllerError(stream.[[controller]], e).
+        [&](JS::NonnullGCPtr<ReadableByteStreamController> controller) {
+            readable_byte_stream_controller_error(controller, error);
+        },
+
+        // 2. Otherwise, perform ! ReadableStreamDefaultControllerError(stream.[[controller]], e).
+        [&](JS::NonnullGCPtr<ReadableStreamDefaultController> controller) {
+            readable_stream_default_controller_error(controller, error);
+        });
+}
+
 void ReadableStream::initialize(JS::Realm& realm)
 {
     Base::initialize(realm);

Userland/Libraries/LibWeb/Streams/ReadableStream.h

@@ -80,6 +80,7 @@ public:
     WebIDL::ExceptionOr<ReadableStreamPair> tee();
 
     void close();
+    void error(JS::Value);
 
     Optional<ReadableStreamController>& controller() { return m_controller; }
     void set_controller(Optional<ReadableStreamController> value) { m_controller = move(value); }