Add equality and empty tests for first_contentful_paint

Add equality and empty tests for first_contentful_paint

ksakamoto discovered that our PageLoadTiming code is missing
equality/empty tests for the first_contentful_paint field.

This means that when FCP is different from FP, and no subsequent
metrics are logged for a given page, FCP may erroneously not get
logged for that page.

BUG=632765
Committed: https://crrev.com/faa55192bc07e10058fef50dfcc3531afeef6a13
Cr-Commit-Position: refs/heads/master@{#408674}

[Bryan McQuade, 2016-07-29 16:28:03]

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

[Bryan McQuade, 2016-07-29 16:28:22]

bmcquade@chromium.org changed reviewers:
+ csharrison@chromium.org

[Bryan McQuade, 2016-07-29 16:28:29]

PTAL

[commit-bot: I haz the power, 2016-07-29 16:28:40]

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

[Charlie Harrison, 2016-07-29 16:54:28]

*sigh* lgtm but I would really love it if we could add some static checks or
unit tests so this wouldn't happen again. Not sure the best way to do that
though. Could be saved for a followup.

[commit-bot: I haz the power, 2016-07-29 17:12:20]

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

[commit-bot: I haz the power, 2016-07-29 17:12:21]

Dry run: This issue passed the CQ dry run.

[Bryan McQuade, 2016-07-29 17:17:17]

The CQ bit was checked by bmcquade@chromium.org

[commit-bot: I haz the power, 2016-07-29 17:17:42]

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, 2016-07-29 17:23:48]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-07-29 17:28:45]

Description was changed from

==========
Add equality and empty tests for first_contentful_paint

ksakamoto discovered that our PageLoadTiming code is missing
equality/empty tests for the first_contentful_paint field.

This means that when FCP is different from FP, and no subsequent
metrics are logged for a given page, FCP may erroneously not get
logged for that page.

BUG=632765
==========

to

==========
Add equality and empty tests for first_contentful_paint

ksakamoto discovered that our PageLoadTiming code is missing
equality/empty tests for the first_contentful_paint field.

This means that when FCP is different from FP, and no subsequent
metrics are logged for a given page, FCP may erroneously not get
logged for that page.

BUG=632765

Committed: https://crrev.com/faa55192bc07e10058fef50dfcc3531afeef6a13
Cr-Commit-Position: refs/heads/master@{#408674}
==========

[commit-bot: I haz the power, 2016-07-29 17:28:46]

Patchset 1 (id:??) landed as
https://crrev.com/faa55192bc07e10058fef50dfcc3531afeef6a13
Cr-Commit-Position: refs/heads/master@{#408674}