Introduce firstRangeOf() as replacement of VisibleSelection::firstRange()

Introduce firstRangeOf() as replacement of VisibleSelection::firstRange()

This patch introduces |firstRangeOf()| function as replacement of |firstRange()|
member function of |VisibleSelection| to prepare templatizing |VisibleSelection|
to exclude DOM tree position specific function out from |VisibleSelection|
for ease of templatizing.

This patch is a preparation of making selection to handle granularity for web
component, http://crrev.com/1277863002

BUG=513568
TEST=n/a; no behavior changes

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=201122

[yosin_UTC9, 2015-08-25 09:24:22]

yosin@chromium.org changed reviewers:
+ tkent@chromium.org

[yosin_UTC9, 2015-08-25 09:24:22]

PTAL

[tkent, 2015-08-25 09:33:28]

lgtm

[yosin_UTC9, 2015-08-25 09:34:01]

The CQ bit was checked by yosin@chromium.org

[commit-bot: I haz the power, 2015-08-25 09:34:14]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1313883002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1313883002/1

[commit-bot: I haz the power, 2015-08-25 10:36:32]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=201122