[viewer] Add angle mtl backend
Since GL is deprecated on Macs, this was the only way I could think to
debug our GL backend with the latest Xcode.
I got some non-Windows EGL usage guidance from
tools/gpu/gl/angle/GLTestContext_angle.cpp, and the proper value to
use for NativeWindowType from github.com/glfw/glfw/pull/1680.
ANGLE Metal documentation seems a little sparse right now.
Change-Id: Ifaaf488b1a2220e366d7d5a70fe0d0db3ca566ec
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/775116
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: James Godfrey-Kittle <jamesgk@google.com>
10 files changed
