Make previousPositionOf() to handle yet another no previous position case

Make previousPositionOf() to handle yet another no previous position case

This patch makes |previousPositionOf()| to handle no previous position case,
which is occurred after visible position canonicalization.

It is time to change |DCEHCK()| to return nothing since we have a test case
for it.

BUG=619131
TEST=run_webkit_unit_tests --gtest_filter=VisibleUnitTests.previousPositionOfNoPreviousPosition

Committed: https://crrev.com/b0ff83a86d043140c423a47c164d43fab5a552bb
Cr-Commit-Position: refs/heads/master@{#403887}

[yosin_UTC9, 2016-07-06 07:43:58]

Description was changed from

==========
2016-07-06T16:42:17

BUG=
==========

to

==========
Make previousPosition() to handle yet another no previous position case


BUG=619131
TEST=run_webkit_unit_tests
--gtest_filter=VisibleUnitTests.previousPositionOfNoPreviousPosition
==========

[yosin_UTC9, 2016-07-06 08:15:30]

Description was changed from

==========
Make previousPosition() to handle yet another no previous position case


BUG=619131
TEST=run_webkit_unit_tests
--gtest_filter=VisibleUnitTests.previousPositionOfNoPreviousPosition
==========

to

==========
Make previousPositionOf() to handle yet another no previous position case

This patch makes |previousPositionOf()| to handle no previous position case,
which is occurred after visible position canonicalization.

It is time to change |DCEHCK()| to return nothing since we have a test case
for it.

BUG=619131
TEST=run_webkit_unit_tests
--gtest_filter=VisibleUnitTests.previousPositionOfNoPreviousPosition
==========

[yosin_UTC9, 2016-07-06 08:16:37]

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

[yosin_UTC9, 2016-07-06 08:16:38]

PTAL

[yoichio, 2016-07-06 09:07:50]

lgtm

[Xiaocheng, 2016-07-06 09:14:56]

lgtm

[yosin_UTC9, 2016-07-06 11:31:45]

The CQ bit was checked by yosin@chromium.org

[commit-bot: I haz the power, 2016-07-06 11:32:03]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-07-06 12:08:25]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-07-06 12:08:30]

CQ bit was unchecked.

[commit-bot: I haz the power, 2016-07-06 12:09:32]

Description was changed from

==========
Make previousPositionOf() to handle yet another no previous position case

This patch makes |previousPositionOf()| to handle no previous position case,
which is occurred after visible position canonicalization.

It is time to change |DCEHCK()| to return nothing since we have a test case
for it.

BUG=619131
TEST=run_webkit_unit_tests
--gtest_filter=VisibleUnitTests.previousPositionOfNoPreviousPosition
==========

to

==========
Make previousPositionOf() to handle yet another no previous position case

This patch makes |previousPositionOf()| to handle no previous position case,
which is occurred after visible position canonicalization.

It is time to change |DCEHCK()| to return nothing since we have a test case
for it.

BUG=619131
TEST=run_webkit_unit_tests
--gtest_filter=VisibleUnitTests.previousPositionOfNoPreviousPosition

Committed: https://crrev.com/b0ff83a86d043140c423a47c164d43fab5a552bb
Cr-Commit-Position: refs/heads/master@{#403887}
==========

[commit-bot: I haz the power, 2016-07-06 12:09:33]

Patchset 1 (id:??) landed as
https://crrev.com/b0ff83a86d043140c423a47c164d43fab5a552bb
Cr-Commit-Position: refs/heads/master@{#403887}