Use EditingTestBase for VisibleSelectionTest

Use EditingTestBase for VisibleSelectionTest

This CL changes TextIteratorTest to inherit EditingTestBase to reduce
duplicated code.

BUG=n/a
TEST=n/a; no behavior change

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=197802

[yosin_UTC9, 2015-06-25 04:57:01]

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

[yosin_UTC9, 2015-06-25 04:57:42]

PTAL

[yoichio, 2015-06-25 05:33:57]

lgtm

[yosin_UTC9, 2015-06-25 05:38:09]

The CQ bit was checked by yosin@chromium.org

[yosin_UTC9, 2015-06-25 09:00:26]

The CQ bit was unchecked by yosin@chromium.org

[yosin_UTC9, 2015-06-25 09:00:27]

The CQ bit was checked by yosin@chromium.org

[yosin_UTC9, 2015-06-25 09:00:33]

The CQ bit was checked by yosin@chromium.org

[commit-bot: I haz the power, 2015-06-25 09:01:09]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1202863003/1

[commit-bot: I haz the power, 2015-06-25 09:07:18]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=197802