Replace ASSERT with DCHECK in Nullable

Replace ASSERT with DCHECK in Nullable

This CL is separate from the others because I want to have a discussion
about possible performance regressions before committing.

BUG=596760
Review-Url: https://codereview.chromium.org/2887883002
Cr-Commit-Position: refs/heads/master@{#472251}
Committed: https://chromium.googlesource.com/chromium/src/+/2679a47b0241a1012b2b0710663993fd6d10ee29

[pilgrim_google, 2017-05-16 18:18:45]

The CQ bit was checked by pilgrim@chromium.org to run a CQ dry run

[pilgrim_google, 2017-05-16 18:18:52]

pilgrim@chromium.org changed reviewers:
+ haraken@chromium.org, tkent@chromium.org

[commit-bot: I haz the power, 2017-05-16 18:20:03]

Dry run: CQ is trying da patch.

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

[haraken, 2017-05-16 20:15:49]

LGTM

[commit-bot: I haz the power, 2017-05-16 20:43:05]

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

[commit-bot: I haz the power, 2017-05-16 20:43:06]

Dry run: This issue passed the CQ dry run.

[pilgrim_google, 2017-05-16 23:18:47]

The CQ bit was checked by pilgrim@chromium.org

[commit-bot: I haz the power, 2017-05-16 23:20:58]

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, 2017-05-16 23:41:03]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1494976727611910, "parent_rev":
"1f3e742fa36fe5d3e8e87f4084a84cf7cd98ad61", "commit_rev":
"2679a47b0241a1012b2b0710663993fd6d10ee29"}

[commit-bot: I haz the power, 2017-05-16 23:41:14]

Description was changed from

==========
Replace ASSERT with DCHECK in Nullable

This CL is separate from the others because I want to have a discussion
about possible performance regressions before committing.

BUG=596760
==========

to

==========
Replace ASSERT with DCHECK in Nullable

This CL is separate from the others because I want to have a discussion
about possible performance regressions before committing.

BUG=596760

Review-Url: https://codereview.chromium.org/2887883002
Cr-Commit-Position: refs/heads/master@{#472251}
Committed:
https://chromium.googlesource.com/chromium/src/+/2679a47b0241a1012b2b07106639...
==========

[commit-bot: I haz the power, 2017-05-16 23:41:15]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/chromium/src/+/2679a47b0241a1012b2b07106639...