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This essentially reverts the following revert:
a599a458.

This reworks the software cache to simplify it and add ability to reuse
larger decoded images instead of always decoding the original image.

R=khushalsagar@chromium.org, ericrk@chromium.org

Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.android:android_optional_gpu_tests_rel
Change-Id: I60d0a6aeb46c136cb8230aa7e1d106ef0386462b
Reviewed-on: https://chromium-review.googlesource.com/783636
Commit-Queue: vmpstr <vmpstr@chromium.org>
Reviewed-by: Eric Karl <ericrk@chromium.org>
Reviewed-by: Khushal <khushalsagar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#523822}