Measure browser->render->browser hop time in UMA.

Measure browser->render->browser hop time in UMA.

Measure AsyncResourceHandler browser->render->browser hop time in UMA to
understand the potential performance benefits of handling redirects entiely in
the browser process instead.

BUG=395552
Committed: https://crrev.com/ed4cc4c4d77e122f8bb8ab92bb70b33bb5f85d57
Cr-Commit-Position: refs/heads/master@{#294165}

[Bence, 2014-09-09 19:22:39]

bnc@chromium.org changed reviewers:
+ asvitkine@chromium.org, davidben@chromium.org

[Bence, 2014-09-09 19:22:40]

asvitkine@chromium.org: Please review changes in
tools/metrics/histograms/histograms.xml. 

davidben@chromium.org: Please review changes in
content/browser/loader/async_resource_handler.{cc,h}.

Thank you.

[davidben, 2014-09-09 21:50:26]

lgtm

[Bence, 2014-09-10 12:25:24]

The CQ bit was checked by bnc@chromium.org

[commit-bot: I haz the power, 2014-09-10 12:26:18]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/bnc@chromium.org/555913002/1

[commit-bot: I haz the power, 2014-09-10 12:35:06]

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

[commit-bot: I haz the power, 2014-09-10 12:35:07]

Try jobs failed on following builders:
  chromium_presubmit on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/chromium_presub...)

[Alexei Svitkine (slow), 2014-09-10 13:36:09]

lgtm

[Bence, 2014-09-10 13:39:13]

The CQ bit was checked by bnc@chromium.org

[commit-bot: I haz the power, 2014-09-10 13:41:54]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/bnc@chromium.org/555913002/1

[commit-bot: I haz the power, 2014-09-10 13:48:10]

Committed patchset #1 (id:1) as d7fae3c208ff9211fff27729c5f7751558cc48f5

[commit-bot: I haz the power, 2014-09-10 13:51:57]

Patchset 1 (id:??) landed as
https://crrev.com/ed4cc4c4d77e122f8bb8ab92bb70b33bb5f85d57
Cr-Commit-Position: refs/heads/master@{#294165}