Tracking bug for enabling webrender on low end intel cherryview devices.

The one I have handy is an atom surface tablet with rather low specs overal

Overall webrender is visibly jankier than non webrender while scrolling. as long as we don't render and only composite, scrolling is smooth, and if we render a handful of tile, scrolling is janky.

Unfortunately, webrender tends to invalidate more than the layers backend for a lot of pages. For example google.com search result pages (search term "test"), have picture cache tiles invalidated constantly during scolling, while it looks like layers manage to invalidate very little.

On the CPU side, the renderer thread is often the bottleneck, with a lot of time spent submitting draw calls (some of which looks like it is sunk into ANGLE's state management code).

Profile taken scrolling towards the bottom of a google search page on the device (towards the bottom, towards the top of the page the sticky header transitions between sticky and not sticky I was trying to avoid that source of invalidation): https://share.firefox.dev/3faV6vG