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In Skia, partially-resident textures of "flipped" textures
occupy texcoords 1 to 1 - h (in Y). In cc, they occupy h to
0. In order to ease interop, we should pick a convention and unify.

I chose the Skia model, since coords can flipped with a
simple 1 - y, which doesn't require knowing the height
of the active region. I also added a new test case for
masks, since the math is a little hinky.

CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1643653002

Cr-Commit-Position: refs/heads/master@{#371930}