Narrow the instrumentation to track jank in HostResolverImpl.

Narrow the instrumentation to track jank in HostResolverImpl.

I am fairly confident this is coming from IsGloballyReachable(), which seems to have a dependency on UDP sockets, so focused the instrumentation there.

One weakness of this instrumentation is it doesn't separate out some of the non-trivial work being done by local variable's destructors (most notably deletion of the UDP sockets, which will likely be hitting issue 165382).

BUG=455942
TBR=pkasting@chromium.org

Committed: https://crrev.com/0eb394e2b9fa06ff225084969300fe65b8f17dfc
Cr-Commit-Position: refs/heads/master@{#327831}

[eroman, 2015-04-30 18:41:58]

eroman@chromium.org changed reviewers:
+ pkasting@chromium.org

[eroman, 2015-04-30 19:54:50]

The CQ bit was checked by eroman@chromium.org

[commit-bot: I haz the power, 2015-04-30 19:56:19]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1120733002/1

[Peter Kasting, 2015-04-30 20:36:54]

In order to measure the effect of local destructors, I often add local scoping
blocks around things to precisely control the destruction time of various
objects, or in the limit make things heap-allocated and then put a ScopedTracker
around the delete statement or similar.

(LGTM)

[commit-bot: I haz the power, 2015-04-30 23:25:53]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-30 23:27:04]

Patchset 1 (id:??) landed as
https://crrev.com/0eb394e2b9fa06ff225084969300fe65b8f17dfc
Cr-Commit-Position: refs/heads/master@{#327831}