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When a PicturePile grows along either axis, the tiles on the edge where
it grew are dropped if any new pixels are added to their recordings.
This means that we need to invalidate them to inform the impl side
about the recording being dropped.

However, if we're going to re-record the tile (it intersects the
interest_rect), then there's no need to invalidate it as the old
recorded pixels remain valid.

Previously we made the assumption that when a PicturePile resized, the
interest rect's center would be to the left and above the old edge of
the pile. However, the interest rect can move at the same time as the
pile is resized, and it can live anywhere with respect to the recording
tiles being dropped.

So we invalidate everything inside the row/column of tiles that were
dropped that is outside of the interest rect by invalidating on all
four sides of the interest rect, but clamping the resulting invalidation
rects to within the dropped tiles row/column.

R=enne
BUG=386998

Review URL: https://codereview.chromium.org/504513002

Cr-Commit-Position: refs/heads/master@{#291762}