Make WebSubstringUtil to use EphemeralRange instead of Range

Make WebSubstringUtil to use EphemeralRange instead of Range

This patch changes |WebSubstringUtil| class to use |EphemeralRange| instead
of |Range| object to avoid registering temporary |Range| object into |Document|
for Oilpan friendly.

This patch is also a preparation of making selection to handle granularity for
web component, http://crrev.com/1277863002 to reduce DOM position dependency
from |VisibleSelection| for ease of templatization of |VisibleSelection|.

BUG=388681, 513568
TEST=n/a; no behavior changes

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=201120

[yosin_UTC9, 2015-08-25 08:57:48]

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

[yosin_UTC9, 2015-08-25 09:05:19]

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

[yosin_UTC9, 2015-08-25 09:05:19]

PTAL

[tkent, 2015-08-25 09:15:19]

lgtm

[yosin_UTC9, 2015-08-25 09:19:52]

The CQ bit was checked by yosin@chromium.org

[commit-bot: I haz the power, 2015-08-25 09:20:02]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1311373002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1311373002/1

[commit-bot: I haz the power, 2015-08-25 10:20:04]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=201120