Manage renderCmdEncoder over lifetime of GrMtlOpsRenderPass.

Rather than create a renderCmdEncoder per draw, we create it up front
and each draw just uses it. On a clear or upload we switch away and
then recreate it.

Bug: skia:
Change-Id: Ic6d612119ed3f7c41183d0186083deae14f96398
Reviewed-by: Greg Daniel <>
Commit-Queue: Jim Van Verth <>
3 files changed