Add time-to-first-contentful-paint to PageLoadMetrics

Add time-to-first-contentful-paint to PageLoadMetrics

This adds PageLoad.Timing2.NavigationToFirstContentfulPaint histogram,
which is the minimum of first text paint and first image paint.

BUG=542943
Committed: https://crrev.com/bff2b1845594947e15222485a7200cd912f01fe5
Cr-Commit-Position: refs/heads/master@{#357032}

[Kunihiko Sakamoto, 2015-10-29 04:10:00]

Description was changed from

==========
WIP

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

to

==========
Add time-to-first-contentful-paint to PageLoadMetrics

This adds PageLoad.Timing2.NavigationToFirstContentfulPaint histogram,
which is the minimum of first text paint and first image paint.

BUG=542943
==========

[Kunihiko Sakamoto, 2015-10-29 04:15:36]

ksakamoto@chromium.org changed reviewers:
+ isherman@chromium.org, kinuko@chromium.org

[kinuko, 2015-10-29 07:14:04]

The code feels a bit tentative but actually I guess we want to try out this and
that for now... so lgtm

https://codereview.chromium.org/1423263003/diff/1/components/page_load_metric...
File components/page_load_metrics/browser/metrics_web_contents_observer.cc
(right):

https://codereview.chromium.org/1423263003/diff/1/components/page_load_metric...
components/page_load_metrics/browser/metrics_web_contents_observer.cc:87:
base::TimeDelta FirstContentfulPaint(const PageLoadTiming& timing) {
naming-nit: GetFirstContent... ?

[Kunihiko Sakamoto, 2015-10-29 08:00:09]

https://codereview.chromium.org/1423263003/diff/1/components/page_load_metric...
File components/page_load_metrics/browser/metrics_web_contents_observer.cc
(right):

https://codereview.chromium.org/1423263003/diff/1/components/page_load_metric...
components/page_load_metrics/browser/metrics_web_contents_observer.cc:87:
base::TimeDelta FirstContentfulPaint(const PageLoadTiming& timing) {
On 2015/10/29 07:14:04, kinuko wrote:
> naming-nit: GetFirstContent... ?
>  

Done.

[Charlie Harrison, 2015-10-29 16:55:43]

On 2015/10/29 08:00:09, Kunihiko Sakamoto wrote:
>
https://codereview.chromium.org/1423263003/diff/1/components/page_load_metric...
> File components/page_load_metrics/browser/metrics_web_contents_observer.cc
> (right):
> 
>
https://codereview.chromium.org/1423263003/diff/1/components/page_load_metric...
> components/page_load_metrics/browser/metrics_web_contents_observer.cc:87:
> base::TimeDelta FirstContentfulPaint(const PageLoadTiming& timing) {
> On 2015/10/29 07:14:04, kinuko wrote:
> > naming-nit: GetFirstContent... ?
> >  
> 
> Done.

lgtm, thanks for adding this.

[Ilya Sherman, 2015-10-29 22:18:58]

histograms lgtm

[Kunihiko Sakamoto, 2015-10-30 01:12:51]

The CQ bit was checked by ksakamoto@chromium.org

[Kunihiko Sakamoto, 2015-10-30 01:12:52]

The patchset sent to the CQ was uploaded after l-g-t-m from kinuko@chromium.org
Link to the patchset: https://codereview.chromium.org/1423263003/#ps20001
(title: "naming")

[commit-bot: I haz the power, 2015-10-30 01:13:32]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1423263003/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1423263003/20001

[commit-bot: I haz the power, 2015-10-30 02:37:58]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-10-30 02:39:42]

Patchset 2 (id:??) landed as
https://crrev.com/bff2b1845594947e15222485a7200cd912f01fe5
Cr-Commit-Position: refs/heads/master@{#357032}