A unified GPU renderer draws a whole page in order

The individual GPU primitives become a complete render path. A single unified renderer walks a page's display list in order and draws each item on the device - the rects, rounded rects, borders, gradients, images, and text all on the GPU, preserving the front-to-back order a page depends on. Anything the GPU path does not yet handle - a drop shadow, a transform, a clip, a filter - is drawn on its own transparent layer by the software renderer and composited in place, so a real, mixed page comes out correct: the common work on the device, only the exotic parts on software. It is proven to match a full software rasterisation within a single level per channel. The GPU aspect moves 22 to 27; making this the default path for live pages, and accelerating WebGL, are the steps that remain. The overall holds at 57.