IDL: Support callback function types in overload resolution

IDL: Support callback function types in overload resolution

The specification has a "if Callable(V) is true, ..." case for (among
other things) callback function types, which is implemented here, only
for callback function types.

BUG=293561
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=185230

[Jens Widell, 2014-11-12 16:31:46]

jl@opera.com changed reviewers:
+ haraken@chromium.org

[Jens Widell, 2014-11-12 16:31:46]

PTAL

No CG changes, since no existing overloads depend on callback function typed
arguments.

[haraken, 2014-11-12 16:35:49]

LGTM

[Jens Widell, 2014-11-12 16:37:13]

The CQ bit was checked by jl@opera.com

[commit-bot: I haz the power, 2014-11-12 16:38:10]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/715353002/1

[commit-bot: I haz the power, 2014-11-12 18:37:41]

Committed patchset #1 (id:1) as 185230