Decouple FileSystem and WebSQL callbacks from VoidCallback and it non-refcounted

Decouple FileSystem and WebSQL callbacks from VoidCallback and make it non-refcounted

Create two new VoidCallback clones in modules/filesystem and modules/webdatabase,
and make the original non-refcounted. This will meet two goals:
  - The only code left using refcounted callbacks are in FileSystem and WebSQL
  - Evolving those two modules' use of callbacks into the modern age should be
    easier now that they're isolated from each other.

R=abarth@chromium.org
BUG=323681
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=163132

[abarth-chromium, 2013-12-03 22:33:41]

lgtm

[commit-bot: I haz the power, 2013-12-03 22:33:51]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/adamk@chromium.org/103083002/1

[commit-bot: I haz the power, 2013-12-04 00:35:27]

Commit queue rejected this change because the description was changed
between the time the change entered the commit queue and the time it
was ready to commit. You can safely check the commit box again.

[adamk, 2013-12-04 01:30:32]

Committed patchset #1 manually as r163132 (presubmit successful).