This large commit also refactors LibWebView's process handling to use
a top-level Application class that uses a new WebView::Process class to
encapsulate the IPC-centric nature of each helper process.
Using mmap-allocated memory for backing stores does not allow us to
benefit from using GPU-accelerated painting, because all the performance
increase we get is mostly negated by reading the GPU-allocated texture
back into RAM, so it can be shared with the browser process.
With IOSurface, we get a framebuffer that is both shareable between
processes and can be used as underlying memory for an OpenGL/Metal
texture.
This change does not yet benefit from using IOSurface and merely wraps
them into Gfx::Bitmap to be used by the CPU painter.
This will be needed to collect statistics from processes that do not
have anything to do with LibWebView. The ProcessInfo structure must be
virtual to allow callers to add application-specific information.
