Revert of Make flow event traces disabled-by-default, and rename "ipc" and "task"

Revert of Make flow event traces disabled-by-default, and rename "ipc" and "task" categories to "toplevel" (https://codereview.chromium.org/148173011/)

Reason for revert:
This is causing a Blink test to fail
The test probably just need to update is expectations.

Original issue's description:
> Make flow event traces disabled-by-default
> 
> Currently all flow events are in the category "toplevel.flow", they originated from "ipc" and "task" categories.
> 
> BUG=338427
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=249450

TBR=nduca@chromium.org,jam@chromium.org,willchan@chromium.org,mark@chromium.org,phajdan.jr@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=341641

[fmeawad, 2014-02-06 23:18:46]

Created Revert of Make flow event traces disabled-by-default, and rename "ipc"
and "task" categories to "toplevel"

[commit-bot: I haz the power, 2014-02-06 23:20:34]

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

[fmeawad, 2014-02-06 23:25:27]

The CQ bit was checked by fmeawad@chromium.org

[commit-bot: I haz the power, 2014-02-06 23:29:36]

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

[commit-bot: I haz the power, 2014-02-06 23:29:37]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM may have been provided, it was from a non-committer or
a lowly provisional committer, _not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.