Fix top-level trace event name in MessageLoop::RunTask

Fix top-level trace event name in MessageLoop::RunTask

... following a typo in https://codereview.chromium.org/1237283006

BUG=523345
TBR=danakj

Committed: https://crrev.com/b20b8680bf5a28b30149e704de43c67a0bbd3354
Cr-Commit-Position: refs/heads/master@{#344928}

[caseq, 2015-08-21 20:25:50]

caseq@chromium.org changed reviewers:
+ beaudoin@chromium.org, nduca@chromium.org

[nduca, 2015-08-21 21:38:36]

lgtm

[beaudoin, 2015-08-21 21:48:50]

LGTM

[caseq, 2015-08-21 22:16:36]

The CQ bit was checked by caseq@chromium.org

[commit-bot: I haz the power, 2015-08-21 22:17:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1305283002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1305283002/1

[commit-bot: I haz the power, 2015-08-21 23:16:30]

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

[commit-bot: I haz the power, 2015-08-21 23:16:30]

Try jobs failed on following builders:
  linux_chromium_chromeos_rel_ng on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[caseq, 2015-08-21 23:17:51]

The CQ bit was checked by caseq@chromium.org

[commit-bot: I haz the power, 2015-08-21 23:18:57]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1305283002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1305283002/1

[commit-bot: I haz the power, 2015-08-22 00:16:13]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-22 00:16:55]

Patchset 1 (id:??) landed as
https://crrev.com/b20b8680bf5a28b30149e704de43c67a0bbd3354
Cr-Commit-Position: refs/heads/master@{#344928}