Support profiling of tasks run as sequenced_tasks

Mimic code seen in message_loop.cc (since these tasks are run on named
threads) to support tracking of sequenced worker pool runs of tasks.
We surround the *.Run() method with a call to get the time before we
start, and then call to tally the time it took to run after task.Run()
returns.


r=brettw
BUG=139035

Review URL: https://chromiumcodereview.appspot.com/10825022

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@148986 0039d316-1c4b-4281-b951-d872f2087c98
3 files changed