cc: Ensure that skewport.Contains(visible_rect) is always true.

cc: Ensure that skewport.Contains(visible_rect) is always true.

This patch ensures that the skewport contains the visible rect. This
is a required that could be violated by extreme visible rects that
would overflow integer math. The fix is to add an extra union.
Includes a test.

R=enne
BUG=487130
Committed: https://crrev.com/7923e436272f671334bc4d75edad97c67bc02212
Cr-Commit-Position: refs/heads/master@{#330600}

[vmpstr, 2015-05-19 19:43:52]

Please take a look.

[enne (OOO), 2015-05-19 19:49:54]

The CQ bit was checked by enne@chromium.org

[enne (OOO), 2015-05-19 19:49:55]

lgtm

[commit-bot: I haz the power, 2015-05-19 19:50:46]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1131383007/1

[commit-bot: I haz the power, 2015-05-19 20:44:39]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-19 20:45:18]

Patchset 1 (id:??) landed as
https://crrev.com/7923e436272f671334bc4d75edad97c67bc02212
Cr-Commit-Position: refs/heads/master@{#330600}