Fix bugs in sheriff-o-matic's pixel zoomer.

Fix bugs in sheriff-o-matic's pixel zoomer.

-x/y were swapped. Create a mock canvas context so we actually
test this code path.
-The zoomer was below the test list. z-index:1 to put it above.

NOTRY=true

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=179073

[leviw_travelin_and_unemployed, 2014-07-28 23:15:23]

lgtm

[ojan, 2014-07-29 00:07:23]

The CQ bit was checked by ojan@chromium.org

[commit-bot: I haz the power, 2014-07-29 00:08:25]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ojan@chromium.org/423703002/1

[commit-bot: I haz the power, 2014-07-29 00:09:15]

Change committed as 179073