Drop const_iterator for AttributeCollection

Drop const_iterator for AttributeCollection

Drop const_iterator for AttributeCollection and use iterator instead as it is
equivalent. AttributeCollection::iterator is inherently const, while
MutableAttributeCollection::iterator isn't.

Since here the constness is defined by the collection type (AttributeCollection
vs MutableAttributeCollection), I don't think we need to distinguish iterator
vs const_iterator. Using iterator everywhere also makes the code a bit shorter.

R=adamk@chromium.org, esprehn@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=179760

[adamk, 2014-08-07 20:32:00]

rslgtm

Given how little iterator usage there is in Blink, opting for shorter code
sounds good to me.

[Inactive, 2014-08-07 20:55:31]

The CQ bit was checked by ch.dumez@samsung.com

[commit-bot: I haz the power, 2014-08-07 20:58:43]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ch.dumez@samsung.com/448043003/1

[commit-bot: I haz the power, 2014-08-07 21:51:15]

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

[commit-bot: I haz the power, 2014-08-07 22:20:55]

Change committed as 179760