Improve VisibleUnitsTest.localCaretRectOfPosition

Improve VisibleUnitsTest.localCaretRectOfPosition

This patch changes |VisibleUnitsTest.localCaretRectOfPosition| to check
results of |localCaretRectOfPosition()| aren't empty for improving detection
of regression.

This is a follow-up patch for http://crrev.com/1317503002, which introduces
composed tree version of | localCaretRectOfPosition()|.

BUG=513568
TEST=webkit_unit_tests --gtest_filter=VisibleUnitsTest.localCaretRectOfPosition

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=201186

[yosin_UTC9, 2015-08-26 02:07:15]

yosin@chromium.org changed reviewers:
+ hajimehoshi@chromium.org, yoichio@chromium.org

[yosin_UTC9, 2015-08-26 02:07:28]

PTAL

[yoichio, 2015-08-26 02:14:37]

lgtm

[yosin_UTC9, 2015-08-26 02:19:12]

The CQ bit was checked by yosin@chromium.org

[commit-bot: I haz the power, 2015-08-26 02:19:30]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1319623004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1319623004/1

[commit-bot: I haz the power, 2015-08-26 02:35:45]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=201186