Replace TraceEvent.begin()/end() with explicit names

Replace TraceEvent.begin()/end() with explicit names

Replace TraceEvent.begin()/end() calls which implicitly gets the trace
event name by doing a costly stack dump, with explicitly named trace
event names.

Also wrap traces around try/finally.

BUG=439118
Committed: https://crrev.com/198d7e12e38a43424fd73f38b8b0270487aba2a0
Cr-Commit-Position: refs/heads/master@{#307974}

[boliu, 2014-12-11 19:07:32]

boliu@chromium.org changed reviewers:
+ boliu@chromium.org

[boliu, 2014-12-11 19:07:33]

lgtm

[mkosiba (inactive), 2014-12-11 19:07:55]

The CQ bit was checked by mkosiba@chromium.org

[commit-bot: I haz the power, 2014-12-11 19:08:06]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/795053007/1

[commit-bot: I haz the power, 2014-12-11 21:05:07]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-12-11 21:05:59]

Patchset 1 (id:??) landed as
https://crrev.com/198d7e12e38a43424fd73f38b8b0270487aba2a0
Cr-Commit-Position: refs/heads/master@{#307974}