Make DragController to use VisibleSelection::toNormalizedEphemeralRange() instead of toNormalizedRan

Make DragController to use VisibleSelection::toNormalizedEphemeralRange() instead of toNormalizedRange()

This patch changes |DragController| class to use |toNormalizedEphemeralRange()|
in |VisibleSelection| class instead of |toNormalizedRange()| as a preparation
of templatizing |VisibleSelection| to use templatized positions instead of
DOM position to represent range.

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=201115

[yosin_UTC9, 2015-08-25 06:00:49]

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

[yosin_UTC9, 2015-08-25 06:01:02]

PTAL

[tkent, 2015-08-25 06:03:22]

lgtm

[yosin_UTC9, 2015-08-25 06:14:25]

The CQ bit was checked by yosin@chromium.org

[commit-bot: I haz the power, 2015-08-25 06:14:38]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1316603002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1316603002/1

[commit-bot: I haz the power, 2015-08-25 06:56:31]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-08-25 06:56:32]

Try jobs failed on following builders:
  mac_chromium_rel_ng on tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_...)

[yosin_UTC9, 2015-08-25 07:41:02]

The CQ bit was checked by yosin@chromium.org

[commit-bot: I haz the power, 2015-08-25 07:41:14]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1316603002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1316603002/1

[commit-bot: I haz the power, 2015-08-25 09:32:03]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=201115