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Previous patch did not update GLTextureRepresentation's clear region
on begin access. This allowed it to get out of sync if other (non-GL)
components modified the clear rect.

This patch updates the cleared rect on each begin access.

Bug: 1039232
Change-Id: Iacc6e65b25d770e1d17e51a5f1c2c632dfad0101
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1990195Reviewed-by: Khushal <khushalsagar@chromium.org>
Reviewed-by: Tommi <tommi@chromium.org>
Commit-Queue: Eric Karl <ericrk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#729950}