Use LazyProxy to set up Metal swapchain.

The purpose of this is to delay acquiring the next drawable in the
swapchain to avoid stalling and gain better parallel execution between
the CPU and GPU.

Change-Id: I40ef7672394fd00616de43685530d2feaf7cab2d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/249005
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
3 files changed