Add iceTransports to RTCConfiguration and add RTCOfferOptions for CreateOffer.

BUG=https://code.google.com/p/webrtc/issues/detail?id=3282

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=178184

Review URL: https://codereview.chromium.org/361093002

git-svn-id: svn://svn.chromium.org/blink/trunk@178197 bbb929c8-8fbe-4397-9dbb-9b2b20218538
WidthIterator cleanup.

First part of https://codereview.chromium.org/383203002/.

* remove unneeded default advance() paramenters

* avoid passing a GlyphBuffer to advance() if the client doesn't actually
  use it (used to be needed internally for kerning and ligature
  adjustments, but we don't support these for simple text - see
  https://codereview.chromium.org/382033002,
  https://codereview.chromium.org/328213002)

* (related to the above) refactor advanceOneCharacter() to no longer
  require a GlyphBuffer

BUG=393279
R=jbroman@chromium.org,eae@chromium.org,schenney@chromium.org

Review URL: https://codereview.chromium.org/387003004

git-svn-id: svn://svn.chromium.org/blink/trunk@178198 bbb929c8-8fbe-4397-9dbb-9b2b20218538