This is a metabug to track Deferred Rendering in GTK+ port. The purpose of Deferred Rendering is to perform rasterization on a dedicated thread to improve performance. Current implementation of WebKit burdens the main thread with many jobs including layout, JavaScript execution, painting, and other heavy jobs. By performing rasterization on a separate thread, we can reduce the responsibilities of the main thread and bring a noticeable performance improvement. For details, refer to the following design document: https://docs.google.com/document/d/1K4q7KtPzsm6c7qUnHqW0NtAv7uItxgs35QZJvHsfLjY/pub Any comments/discussions are appreciated.