Make textDistance() in SelectionController not to create a redundant Range object

Make textDistance() in SelectionController not to create a redundant Range object

This patch makes |textDisatnce()| in "SelectionController.cpp" not to create
a redundant Range object.

This patch is result of collaboration work with hajimehoshi@chromium.org
for selection of web components. After this patch, we are going to
implement another strategies for the composed tree. We've already
prepared that at http://crrev.com/1106433002.

BUG=275851
TEST=n/a; No behavior changes.

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=197456

[yosin_UTC9, 2015-06-19 07:08:56]

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

[yosin_UTC9, 2015-06-19 07:42:21]

PTAL

[tkent, 2015-06-19 07:57:39]

The CQ bit was checked by tkent@chromium.org

[tkent, 2015-06-19 07:57:39]

lgtm

[commit-bot: I haz the power, 2015-06-19 07:57:56]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1190283002/1

[commit-bot: I haz the power, 2015-06-19 08:26:15]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=197456