Move HTMLTable*Element.insert{Row,Cell}'s argument default into IDL file

Move HTMLTable*Element.insert{Row,Cell}'s argument default into IDL file

They each take an index argument, that should default to -1.

This matches the specification, and doesn't change behavior since these
defaults were already implemented in the C++ code.

BUG=258153
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=180656

[Jens Widell, 2014-08-20 13:04:55]

And another one... :-)

[haraken, 2014-08-20 13:37:54]

LGTM

[Jens Widell, 2014-08-20 14:04:57]

The CQ bit was checked by jl@opera.com

[commit-bot: I haz the power, 2014-08-20 14:05:09]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/jl@opera.com/494653002/1

[commit-bot: I haz the power, 2014-08-20 15:01:51]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  win_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/23649)

[commit-bot: I haz the power, 2014-08-20 15:39:49]

Committed patchset #1 (1) as 180656