Fix 3 more leaks in WebPluginContainerTests.

Fix 3 more leaks in WebPluginContainerTests.

I missed LocalToWindowPointTest in https://codereview.chromium.org/1308663004/,
and there are two more tests with different subclasses too.

BUG=523910
TBR=chrishtr

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=201521

[Nico, 2015-09-01 04:32:14]

thakis@chromium.org changed reviewers:
+ chrishtr@chromium.org

[Nico, 2015-09-01 04:32:14]

Since this is morally the same change as
https://codereview.chromium.org/1308663004/ and since the leak bot I'm looking
at takes some 6h to cycle, I'll tbr this, in the hope that the cq lands it and I
have results tomorrow morning. Please do take a look, and I'm happy to address
comments in a follow-up :-)

[Nico, 2015-09-01 04:32:18]

The CQ bit was checked by thakis@chromium.org

[commit-bot: I haz the power, 2015-09-01 04:32:30]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1314353004/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1314353004/20001

[Nico, 2015-09-01 05:22:07]

Committed patchset #2 (id:20001) manually as 201521 (presubmit successful).

[chrishtr, 2015-09-01 18:06:43]

lgtm