DevTools: extract PollManager from SASSSourceMapping

DevTools: extract PollManager from SASSSourceMapping

Extract all logic responsible for polling of a newly generated CSS
file into a separate PollManager file.

BUG=527993
R=pfeldman
NOTRY=true

Committed: https://crrev.com/3fd3203298731b47238c1e2832b6c4198d37d570
git-svn-id: svn://svn.chromium.org/blink/trunk@202312 bbb929c8-8fbe-4397-9dbb-9b2b20218538

[lushnikov, 2015-09-15 20:48:31]

ptal

[pfeldman, 2015-09-15 21:45:29]

lgtm

[lushnikov, 2015-09-15 21:47:32]

The CQ bit was checked by lushnikov@chromium.org

[commit-bot: I haz the power, 2015-09-15 21:48:13]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1344833004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1344833004/1

[commit-bot: I haz the power, 2015-09-15 23:51:39]

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

[commit-bot: I haz the power, 2015-09-15 23:51:40]

Try jobs failed on following builders:
  win_chromium_rel_ng on tryserver.chromium.win (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel_...)

[lushnikov, 2015-09-15 23:54:01]

The CQ bit was checked by lushnikov@chromium.org

[commit-bot: I haz the power, 2015-09-15 23:54:20]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1344833004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1344833004/1

[commit-bot: I haz the power, 2015-09-16 01:41:31]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=202312

[commit-bot: I haz the power, 2015-09-23 12:52:46]

Patchset 1 (id:??) landed as
https://crrev.com/3fd3203298731b47238c1e2832b6c4198d37d570