Log an immediate variant of FirstContentfulPaint

Log an immediate variant of FirstContentfulPaint.

Our page load metrics are currently logged at the time a page is 'closed'.
For example, when a tab is closed, or when a page is navigated away from.
If a page stays open for a long period of time, we may log its metrics long
after the events for those metrics occurred. This may cause issues such as
logging metrics for events that happened on WiFi later, when the user is on
2G, or vice versa. We don't know how much of a problem this is, so to start,
we're adding a single metric to allow us to track the difference between
logging at the end of a page load and logging immediately after the page
event occurred. If the difference is significant, this may motivate us to
migrate other events to more immediate logging.

BUG=609660
Committed: https://crrev.com/3e0a460bd23c5c2e25b8bf6b9813f8c78408a595
Cr-Commit-Position: refs/heads/master@{#392330}

[Bryan McQuade, 2016-05-05 23:43:41]

Description was changed from

==========
Prototype incremental core page load metrics logging.

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

to

==========
Log an immediate variant of FirstContentfulPaint.

Our page load metrics are currently logged at the time a page is 'closed'.
For example, when a tab is closed, or when a page is navigated away from.
If a page stays open for a long period of time, we may log its metrics long
after the events for those metrics occurred. This may cause issues such as
logging metrics for events that happened on WiFi later, when the user is on
2G, or vice versa. We don't know how much of a problem this is, so to start,
we're adding a single metric to allow us to track the difference between
logging at the end of a page load and logging immediately after the page
event occurred. If the difference is significant, this may motivate us to
migrate other events to more immediate logging.

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

[Bryan McQuade, 2016-05-06 00:05:15]

Description was changed from

==========
Log an immediate variant of FirstContentfulPaint.

Our page load metrics are currently logged at the time a page is 'closed'.
For example, when a tab is closed, or when a page is navigated away from.
If a page stays open for a long period of time, we may log its metrics long
after the events for those metrics occurred. This may cause issues such as
logging metrics for events that happened on WiFi later, when the user is on
2G, or vice versa. We don't know how much of a problem this is, so to start,
we're adding a single metric to allow us to track the difference between
logging at the end of a page load and logging immediately after the page
event occurred. If the difference is significant, this may motivate us to
migrate other events to more immediate logging.

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

to

==========
Log an immediate variant of FirstContentfulPaint.

Our page load metrics are currently logged at the time a page is 'closed'.
For example, when a tab is closed, or when a page is navigated away from.
If a page stays open for a long period of time, we may log its metrics long
after the events for those metrics occurred. This may cause issues such as
logging metrics for events that happened on WiFi later, when the user is on
2G, or vice versa. We don't know how much of a problem this is, so to start,
we're adding a single metric to allow us to track the difference between
logging at the end of a page load and logging immediately after the page
event occurred. If the difference is significant, this may motivate us to
migrate other events to more immediate logging.

BUG=609660
==========

[Bryan McQuade, 2016-05-06 00:05:41]

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

[Bryan McQuade, 2016-05-06 00:07:30]

PTAL

[Charlie Harrison, 2016-05-06 18:13:38]

LGTM. You could also make "Immediate" a histogram suffix, but it doesn't really
matter to me.

[Bryan McQuade, 2016-05-06 18:26:08]

On 2016/05/06 at 18:13:38, csharrison wrote:
> LGTM. You could also make "Immediate" a histogram suffix, but it doesn't
really matter to me.

Yeah, that's a good point, I think suffixes are a better approach here. I've
switched. Thanks!

[Bryan McQuade, 2016-05-06 18:27:03]

https://codereview.chromium.org/1953673003/diff/80001/tools/metrics/histogram...
File tools/metrics/histograms/histograms.xml (right):

https://codereview.chromium.org/1953673003/diff/80001/tools/metrics/histogram...
tools/metrics/histograms/histograms.xml:35545: +    The time from navigation
start to first "contentful" paint.
note: the latter part of the description was no longer accurate, so i removed
it.

[Bryan McQuade, 2016-05-06 18:27:23]

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

[Bryan McQuade, 2016-05-06 18:27:33]

asvitkine, PTAL for histograms.xml.

[Charlie Harrison, 2016-05-06 18:28:30]

still lgtm.

[Alexei Svitkine (slow), 2016-05-09 16:24:24]

lgtm

[Bryan McQuade, 2016-05-09 16:24:41]

The CQ bit was checked by bmcquade@chromium.org

[Bryan McQuade, 2016-05-09 16:24:41]

The patchset sent to the CQ was uploaded after l-g-t-m from
csharrison@chromium.org
Link to the patchset: https://codereview.chromium.org/1953673003/#ps160001
(title: " add tests")

[commit-bot: I haz the power, 2016-05-09 16:25:07]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1953673003/160001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1953673003/160001

[commit-bot: I haz the power, 2016-05-09 16:29:19]

Committed patchset #9 (id:160001)

[commit-bot: I haz the power, 2016-05-09 16:31:17]

Description was changed from

==========
Log an immediate variant of FirstContentfulPaint.

Our page load metrics are currently logged at the time a page is 'closed'.
For example, when a tab is closed, or when a page is navigated away from.
If a page stays open for a long period of time, we may log its metrics long
after the events for those metrics occurred. This may cause issues such as
logging metrics for events that happened on WiFi later, when the user is on
2G, or vice versa. We don't know how much of a problem this is, so to start,
we're adding a single metric to allow us to track the difference between
logging at the end of a page load and logging immediately after the page
event occurred. If the difference is significant, this may motivate us to
migrate other events to more immediate logging.

BUG=609660
==========

to

==========
Log an immediate variant of FirstContentfulPaint.

Our page load metrics are currently logged at the time a page is 'closed'.
For example, when a tab is closed, or when a page is navigated away from.
If a page stays open for a long period of time, we may log its metrics long
after the events for those metrics occurred. This may cause issues such as
logging metrics for events that happened on WiFi later, when the user is on
2G, or vice versa. We don't know how much of a problem this is, so to start,
we're adding a single metric to allow us to track the difference between
logging at the end of a page load and logging immediately after the page
event occurred. If the difference is significant, this may motivate us to
migrate other events to more immediate logging.

BUG=609660

Committed: https://crrev.com/3e0a460bd23c5c2e25b8bf6b9813f8c78408a595
Cr-Commit-Position: refs/heads/master@{#392330}
==========

[commit-bot: I haz the power, 2016-05-09 16:31:18]

Patchset 9 (id:??) landed as
https://crrev.com/3e0a460bd23c5c2e25b8bf6b9813f8c78408a595
Cr-Commit-Position: refs/heads/master@{#392330}