QUIC - Record loading of QUICServerInfo from disk cache.

QUIC - Record loading of QUICServerInfo from disk cache.

Added Net.QuicServerInfo.DiskCacheLoadTime histogram to track the read
time.

R=asvitkine@chromium.org, rch@chromium.org

Committed: https://crrev.com/6ab66362b09827c5e93e574a2aa13519272812fe
Cr-Commit-Position: refs/heads/master@{#300710}

[ramant (doing other things), 2014-10-22 00:28:37]

rtenneti@chromium.org changed reviewers:
+ asvitkine@chromium.org, rch@chromium.org

[ramant (doing other things), 2014-10-22 00:38:05]

The following are the different times we are measuring. DiskCacheLoadTime will
be less than HostResolutionTime + DiskCacheWaitForDataReadyTime.

<------- DiskCacheLoadTime ------->
<-- HostResolutionTime --><--DiskCacheWaitForDataReadyTime-->

Network speed (host resolution), disk speed, disk cache hit/miss determine
HostResolutionTime and DiskCacheLoadTime times.

[Ryan Hamilton, 2014-10-22 02:56:01]

lgtm

[Alexei Svitkine (slow), 2014-10-22 15:08:12]

lgtm

[ramant (doing other things), 2014-10-22 16:43:06]

The CQ bit was checked by rtenneti@chromium.org

[commit-bot: I haz the power, 2014-10-22 16:46:04]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/674453003/1

[commit-bot: I haz the power, 2014-10-22 18:25:26]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-10-22 18:26:58]

Patchset 1 (id:??) landed as
https://crrev.com/6ab66362b09827c5e93e574a2aa13519272812fe
Cr-Commit-Position: refs/heads/master@{#300710}