cc: Do the math for a tile's content rect in layer space once.

cc: Do the math for a tile's content rect in layer space once.

We currently do this math in CoversRect(), GatherPixelRefs() and each
time a tile is rastered to compute damage. We also do this multiple
times in the process of creating a tile.

We can do this once at the time we create the tile and pass it around
and store it on the Tile instead. Less math!

R=vmpstr
BUG=342848
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1318733006

Cr-Commit-Position: refs/heads/master@{#346491}