Reland "Changes to build inside a Dawn checkout." This is a reland of 11c31e0a4a73d7d62e765dc7ec400560fbb16b5e I've landed upstream Skia change https://skia-review.googlesource.com/c/skia/+/351496 which should make this safe to reland. Original change's description: > Changes to build inside a Dawn checkout. > > Add an "angle_standalone" flag that can be disabled by Dawn. > Put test definitions behind angle_standalone || build_with_chromium. > > Bug: angleproject:5462 > Change-Id: I58c9b18723384334156e2a3dd86ed3f89afcaade > Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2587451 > Reviewed-by: Jamie Madill <jmadill@chromium.org> > Commit-Queue: Stephen White <senorblanco@chromium.org> Bug: angleproject:5462 Change-Id: I4ff92d45b3692312a004f03b425234b78c5a6219 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2618040 Commit-Queue: Stephen White <senorblanco@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>