Add histogram to track overhead for scanning external css

Add histogram to track overhead for scanning external css

This patch adds a histogram to count the microseconds used to preload
scan the first chunk of CSS for the @import scanning experiment.

BUG=596676
Committed: https://crrev.com/dee540ca7dff49cf44ed84443e2d266e462e2c52
Cr-Commit-Position: refs/heads/master@{#414787}

[Charlie Harrison, 2016-08-26 13:53:00]

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

[commit-bot: I haz the power, 2016-08-26 13:53:23]

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

[Charlie Harrison, 2016-08-26 13:54:14]

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

[Charlie Harrison, 2016-08-26 13:54:15]

Kouhei, do you think the copy+scan of the first chunk of css could take over 1
second? I wanted to go for microsecond resolution here because usually this
should be quite fast.

[kouhei (in TOK), 2016-08-26 15:17:34]

lgtm

[Charlie Harrison, 2016-08-26 15:22:31]

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

[Charlie Harrison, 2016-08-26 15:22:32]

Thanks! +mpearson for histograms.xml review.

[commit-bot: I haz the power, 2016-08-26 15:55:57]

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

[commit-bot: I haz the power, 2016-08-26 15:55:58]

Dry run: This issue passed the CQ dry run.

[Mark P, 2016-08-26 18:04:07]

lgtm

[Charlie Harrison, 2016-08-26 19:46:27]

The CQ bit was checked by csharrison@chromium.org

[commit-bot: I haz the power, 2016-08-26 19:47:03]

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, 2016-08-26 19:52:10]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-08-26 19:54:18]

Description was changed from

==========
Add histogram to track overhead for scanning external css

This patch adds a histogram to count the microseconds used to preload
scan the first chunk of CSS for the @import scanning experiment.

BUG=596676
==========

to

==========
Add histogram to track overhead for scanning external css

This patch adds a histogram to count the microseconds used to preload
scan the first chunk of CSS for the @import scanning experiment.

BUG=596676

Committed: https://crrev.com/dee540ca7dff49cf44ed84443e2d266e462e2c52
Cr-Commit-Position: refs/heads/master@{#414787}
==========

[commit-bot: I haz the power, 2016-08-26 19:54:19]

Patchset 2 (id:??) landed as
https://crrev.com/dee540ca7dff49cf44ed84443e2d266e462e2c52
Cr-Commit-Position: refs/heads/master@{#414787}