Revert of Remove ChromiumSvnPoller

Revert of Remove ChromiumSvnPoller (patchset #1 id:1 of https://codereview.chromium.org/2284403002/ )

Reason for revert:
This broke botmap_updater, because it is still used by at least one official master - see http://crbug.com/642448 (internal only).

Original issue's description:
> Remove ChromiumSvnPoller
> 
> This is unused now.
> 
> BUG=640212
> 
> Committed: https://chromium.googlesource.com/chromium/tools/build/+/a7625a98f986527265f39add33590853ddaaf761

TBR=tandrii@chromium.org,agable@chromium.org,maruel@chromium.org,machenbach@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=640212

[Sergey Berezin, 2016-08-30 21:28:59]

The CQ bit was checked by sergeyberezin@chromium.org

[Sergey Berezin, 2016-08-30 21:29:00]

Created Revert of Remove ChromiumSvnPoller

[commit-bot: I haz the power, 2016-08-30 21:29:11]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[M-A Ruel, 2016-08-30 21:30:03]

Dropping a tear...

[tandrii(chromium), 2016-08-30 21:30:19]

LGTM, thanks!

[tandrii(chromium), 2016-08-30 21:31:25]

The CQ bit was unchecked by tandrii@chromium.org

[tandrii(chromium), 2016-08-30 21:31:44]

I can fix the internal master with one liner...

[Sergey Berezin, 2016-08-30 21:33:29]

On 2016/08/30 at 21:31:44, tandrii wrote:
> I can fix the internal master with one liner...

Sure, please do! I'm all for re-landing this if we are sure nobody actually uses
it (I'll post a command on a bug that actually failed - for easy testing)

[tandrii(chromium), 2016-08-30 21:33:44]

On 2016/08/30 21:31:44, tandrii(chromium) wrote:
> I can fix the internal master with one liner...

here: https://chromereviews.googleplex.com/499777014

[agable, 2016-08-30 21:34:20]

On 2016/08/30 at 21:33:29, sergeyberezin wrote:
> On 2016/08/30 at 21:31:44, tandrii wrote:
> > I can fix the internal master with one liner...
> 
> Sure, please do! I'm all for re-landing this if we are sure nobody actually
uses it (I'll post a command on a bug that actually failed - for easy testing)

Yeah let's fix this rather than revert, it'll be super fast. Please cc me on the
fix CL.

[agable, 2016-08-30 21:37:45]

Woohoo, y'all are fast! Closing this, replaced by
https://chromereviews.googleplex.com/499777014