Introduce EditingTestBase to share code among test files for editing

Introduce EditingTestBase to share code among test files for editing

This patch introduces |EditingTestBase| class for GTest base unit tests to share
code among test files for avoiding code cloning.

Following patches will utilize this class into:
 - PositionTest.cpp
 - StyledMarkupSerializerTest.cpp
 - VisibleSelection.cpp
 - VisibleUnits.cpp

BUGS=n/a
TESTS=no behavior changes

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=197710

[yosin_UTC9, 2015-06-24 02:13:07]

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

[yosin_UTC9, 2015-06-24 02:13:54]

PTAL

[tkent, 2015-06-24 02:18:05]

The CQ bit was checked by tkent@chromium.org

[tkent, 2015-06-24 02:18:05]

lgtm

[commit-bot: I haz the power, 2015-06-24 02:18:22]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1204953002/1

[commit-bot: I haz the power, 2015-06-24 03:24:35]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-06-24 03:24:36]

Try jobs failed on following builders:
  mac_blink_rel on tryserver.blink (JOB_FAILED,
http://build.chromium.org/p/tryserver.blink/builders/mac_blink_rel/builds/60485)

[yosin_UTC9, 2015-06-24 03:24:50]

The CQ bit was checked by yosin@chromium.org

[commit-bot: I haz the power, 2015-06-24 03:25:07]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1204953002/1

[yosin_UTC9, 2015-06-24 03:35:34]

The CQ bit was unchecked by yosin@chromium.org

[yosin_UTC9, 2015-06-24 03:48:20]

The CQ bit was checked by yosin@chromium.org

[yosin_UTC9, 2015-06-24 03:48:20]

The patchset sent to the CQ was uploaded after l-g-t-m from tkent@chromium.org
Link to the patchset: https://codereview.chromium.org/1204953002/#ps20001
(title: "2015-06-24T12:46:38 Add missing |static| keyword.")

[commit-bot: I haz the power, 2015-06-24 03:48:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1204953002/20001

[commit-bot: I haz the power, 2015-06-24 05:04:59]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-06-24 05:05:00]

Try jobs failed on following builders:
  mac_blink_rel on tryserver.blink (JOB_FAILED,
http://build.chromium.org/p/tryserver.blink/builders/mac_blink_rel/builds/60504)

[yosin_UTC9, 2015-06-24 05:10:27]

The CQ bit was checked by yosin@chromium.org

[commit-bot: I haz the power, 2015-06-24 05:10:34]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1204953002/20001

[commit-bot: I haz the power, 2015-06-24 06:30:19]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-06-24 06:30:20]

Try jobs failed on following builders:
  mac_blink_rel on tryserver.blink (JOB_FAILED,
http://build.chromium.org/p/tryserver.blink/builders/mac_blink_rel/builds/60512)

[yosin_UTC9, 2015-06-24 06:34:14]

The CQ bit was checked by yosin@chromium.org

[yosin_UTC9, 2015-06-24 06:34:15]

The patchset sent to the CQ was uploaded after l-g-t-m from tkent@chromium.org
Link to the patchset: https://codereview.chromium.org/1204953002/#ps40001
(title: "2015-06-24T15:31:52 Rebase for chaning bot(?)")

[commit-bot: I haz the power, 2015-06-24 06:34:21]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1204953002/40001

[commit-bot: I haz the power, 2015-06-24 07:31:12]

Committed patchset #3 (id:40001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=197710