Add histogram to track Mojo shell / renderer connection init

Add histogram to track Mojo shell / renderer connection init

Renderer startup blocks on initializing its shell connection, so this
needs to be fast. Here's some data to monitor.

BUG=591742
Committed: https://crrev.com/fcf7354b33a5df1f26cee7c2da9b7c4864897679
Cr-Commit-Position: refs/heads/master@{#379691}

[Ken Rockot(use gerrit already), 2016-03-07 20:34:06]

rockot@chromium.org changed reviewers:
+ ben@chromium.org, isherman@chromium.org

[Ken Rockot(use gerrit already), 2016-03-07 20:34:07]

isherman@ please take a look at histograms.xml

ben@ for general review

[Ben Goodger (Google), 2016-03-07 21:43:12]

lgtm

[Ilya Sherman, 2016-03-07 22:08:32]

https://codereview.chromium.org/1768363002/diff/1/content/renderer/renderer_m...
File content/renderer/renderer_main.cc (right):

https://codereview.chromium.org/1768363002/diff/1/content/renderer/renderer_m...
content/renderer/renderer_main.cc:16: #include "base/metrics/histogram.h"
nit: Do you need both the histogram and the histogram_macros includes?

https://codereview.chromium.org/1768363002/diff/1/content/renderer/renderer_m...
content/renderer/renderer_main.cc:102: timer.Elapsed());
Are you sure you want a *local* histogram, i.e. one that is not uploaded to UMA?
 What's the expected use for this data?

https://codereview.chromium.org/1768363002/diff/1/tools/metrics/histograms/hi...
File tools/metrics/histograms/histograms.xml (right):

https://codereview.chromium.org/1768363002/diff/1/tools/metrics/histograms/hi...
tools/metrics/histograms/histograms.xml:21936: +<histogram
name="Mojo.Shell.RenderProcessInitializationTime" units="ms">
If you're defining a local histogram, there's no need to add it to
histograms.xml.  (Though, I guess it doesn't hurt, either.)

https://codereview.chromium.org/1768363002/diff/1/tools/metrics/histograms/hi...
tools/metrics/histograms/histograms.xml:21940: +    initialization request from
the Mojo shell.
nit: It might be nice to be super duper specific about what the start and end
events are.  A lot of our timing metrics seem like they should be obvious, but
then people end up getting confused because they make slightly different
assumptions about what exactly is being measured.

[Ken Rockot(use gerrit already), 2016-03-07 22:24:50]

https://codereview.chromium.org/1768363002/diff/1/content/renderer/renderer_m...
File content/renderer/renderer_main.cc (right):

https://codereview.chromium.org/1768363002/diff/1/content/renderer/renderer_m...
content/renderer/renderer_main.cc:16: #include "base/metrics/histogram.h"
On 2016/03/07 at 22:08:32, Ilya Sherman wrote:
> nit: Do you need both the histogram and the histogram_macros includes?

Doubtful - I've removed histogram.h

https://codereview.chromium.org/1768363002/diff/1/content/renderer/renderer_m...
content/renderer/renderer_main.cc:102: timer.Elapsed());
On 2016/03/07 at 22:08:32, Ilya Sherman wrote:
> Are you sure you want a *local* histogram, i.e. one that is not uploaded to
UMA?  What's the expected use for this data?

No! Good catch, I wanted an UMA histogram. Fixed.

https://codereview.chromium.org/1768363002/diff/1/tools/metrics/histograms/hi...
File tools/metrics/histograms/histograms.xml (right):

https://codereview.chromium.org/1768363002/diff/1/tools/metrics/histograms/hi...
tools/metrics/histograms/histograms.xml:21940: +    initialization request from
the Mojo shell.
On 2016/03/07 at 22:08:32, Ilya Sherman wrote:
> nit: It might be nice to be super duper specific about what the start and end
events are.  A lot of our timing metrics seem like they should be obvious, but
then people end up getting confused because they make slightly different
assumptions about what exactly is being measured.

Added some details.

[Ilya Sherman, 2016-03-08 00:19:43]

LGTM, thanks.

[Ken Rockot(use gerrit already), 2016-03-08 00:27:29]

The CQ bit was checked by rockot@chromium.org

[Ken Rockot(use gerrit already), 2016-03-08 00:27:29]

The patchset sent to the CQ was uploaded after l-g-t-m from ben@chromium.org
Link to the patchset: https://codereview.chromium.org/1768363002/#ps20001
(title: " ")

[commit-bot: I haz the power, 2016-03-08 00:28:10]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1768363002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1768363002/20001

[commit-bot: I haz the power, 2016-03-08 00:55:22]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-03-08 00:56:20]

Description was changed from

==========
Add histogram to track Mojo shell / renderer connection init

Renderer startup blocks on initializing its shell connection, so this
needs to be fast. Here's some data to monitor.

BUG=591742
==========

to

==========
Add histogram to track Mojo shell / renderer connection init

Renderer startup blocks on initializing its shell connection, so this
needs to be fast. Here's some data to monitor.

BUG=591742

Committed: https://crrev.com/fcf7354b33a5df1f26cee7c2da9b7c4864897679
Cr-Commit-Position: refs/heads/master@{#379691}
==========

[commit-bot: I haz the power, 2016-03-08 00:56:21]

Patchset 2 (id:??) landed as
https://crrev.com/fcf7354b33a5df1f26cee7c2da9b7c4864897679
Cr-Commit-Position: refs/heads/master@{#379691}