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With overlay forwarding using wl_subsurface, a wl_buffer can be cropped
and scaled to fit a display_rect. This CL adds the extension
wp_viewporter to enable crop&scale, as well as buffer_transform.
When calculating surface-local damage, take into account
buffer_transform, crop and scale.

This is 5/? CL for overlay forwarding using wl_subsurface.

Bug: 1063865
Change-Id: I5cd0a28b7043557aeca0664f59152fd05eadf885
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2327636Reviewed-by: Robert Kroeger <rjkroege@chromium.org>
Reviewed-by: Maksim Sisov (GMT+3) <msisov@igalia.com>
Commit-Queue: Kramer Ge <fangzhoug@chromium.org>
Cr-Commit-Position: refs/heads/master@{#810259}