Revert of Move tracing namespace from base::debug to base::trace_event.

Revert of Move tracing namespace from base::debug to base::trace_event. (patchset #7 id:120001 of https://codereview.chromium.org/882673002/)

Reason for revert:
broken Memory.FYI TSan bot.
crbug.com/455530

Original issue's description:
> Move tracing namespace from base::debug to base::trace_event.
>
> After having transitioned all the tracing headers from base/debug/ to
> base/trace_event, this CL addresses the namespace move.
> In principle, this CL should only change the namespace of the
> base/trace_event files but the namespace used by the tracing clients.
> In order to achieve this, namespace aliases are appended to the
> trace_event headers, to make it so that clients can still refer to
> base::debug::TraceFoo, with that being aliased to
> base::trace_event::TraceFoo.
> The upcoming CLs will gradually migrate the clients to use the
> base::trace_event namespace and will remove the ns aliases.
> Unfortunately, this CL has also to update few tracing clients,
> in particular the ones having forward declarations. Forward
> declarations, in fact, cannot be aliased as the compiler sees them
> before the alias itself.
>
> See crrev.com/837303004 and the related bug for motivations and design doc.
>
> BUG=451032
> TBR=skyostil@chromium.org,jam@chromium.org
>
> Committed: https://crrev.com/97c5abba36f5ce473cd996fab74fbf5aa9bb5464
> Cr-Commit-Position: refs/heads/master@{#314657}

TBR=dsinclair@chromium.org,picksi@chromium.org,primiano@chromium.org,skyostil@chromium.org,ssid@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=451032
Committed: https://crrev.com/c7c37ff30cd9dbacfaef0eef5a6b2b53cdae905c
Cr-Commit-Position: refs/heads/master@{#314740}

[zhaoqin1, 2015-02-05 03:49:54]

Created Revert of Move tracing namespace from base::debug to base::trace_event.

[commit-bot: I haz the power, 2015-02-05 03:50:14]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/904573002/1

[commit-bot: I haz the power, 2015-02-05 03:51:31]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-05 03:52:52]

Patchset 1 (id:??) landed as
https://crrev.com/c7c37ff30cd9dbacfaef0eef5a6b2b53cdae905c
Cr-Commit-Position: refs/heads/master@{#314740}