Support forcing all screenshots into a CPU consumer

Looks like a full GPU path is less efficient on some GPU
drivers that we're still using, and CPU is reliably faster...
(there's probably a locking condition going on somewhere, this
needs to be looked into)

Change-Id: I8878796a117d65bf2324507cf8755cadce49f6dc
libEGL: allow devices to workaround Google bug 10194508

Most older blobs don't have the EGL_KHR_gl_colorspace
extension and need this workaround.

Change-Id: Ifc5d097c1a0b68275d23c2d191976ac96631b695