AstValueFactory: Add paranoid null checks for debugging.

AstValueFactory: Add paranoid null checks for debugging.

crbug.com/518788 looks like AstValueFactory::strings_ would contain
nullptrs which shouldn't be possible. This CL makes us crash earlier
before putting nullptrs into it. It's paranoid, since Zone should
already crash before returning nullptr.

BUG=518788
LOG=n
R=adamk@chromium.org

Committed: https://crrev.com/3e5872f1e1070b36077c8d079f3850fa6510872a
Cr-Commit-Position: refs/heads/master@{#37817}

[marja, 2016-07-15 08:01:11]

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

[commit-bot: I haz the power, 2016-07-15 08:01:17]

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

[marja, 2016-07-15 08:01:54]

adamk, ptal

I'd just want to see whether the crash moves into this line, if yes, then the
theory "string_ contained nullptrs" was true. If not, then it's something else.

[commit-bot: I haz the power, 2016-07-15 08:27:21]

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

[commit-bot: I haz the power, 2016-07-15 08:27:21]

Dry run: This issue passed the CQ dry run.

[adamk, 2016-07-15 18:24:11]

lgtm

This might regress perf somewhere, but we can always revert after we get some
data from the field.

[marja, 2016-07-18 07:36:03]

The CQ bit was checked by marja@chromium.org

[commit-bot: I haz the power, 2016-07-18 07:36:14]

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, 2016-07-18 08:06:36]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-07-18 08:08:55]

Description was changed from

==========
AstValueFactory: Add paranoid null checks for debugging.

crbug.com/518788 looks like AstValueFactory::strings_ would contain
nullptrs which shouldn't be possible. This CL makes us crash earlier
before putting nullptrs into it. It's paranoid, since Zone should
already crash before returning nullptr.

BUG=518788
LOG=n
R=adamk@chromium.org
==========

to

==========
AstValueFactory: Add paranoid null checks for debugging.

crbug.com/518788 looks like AstValueFactory::strings_ would contain
nullptrs which shouldn't be possible. This CL makes us crash earlier
before putting nullptrs into it. It's paranoid, since Zone should
already crash before returning nullptr.

BUG=518788
LOG=n
R=adamk@chromium.org

Committed: https://crrev.com/3e5872f1e1070b36077c8d079f3850fa6510872a
Cr-Commit-Position: refs/heads/master@{#37817}
==========

[commit-bot: I haz the power, 2016-07-18 08:08:56]

Patchset 1 (id:??) landed as
https://crrev.com/3e5872f1e1070b36077c8d079f3850fa6510872a
Cr-Commit-Position: refs/heads/master@{#37817}