Templatize LayoutView::commitPendingSelection function

Templatize LayoutView::commitPendingSelection function

This patch introduces a template function |commitPendingSelectionAlgorithm<Startegy>|
to makes |LayoutView::commitPendingSelection()| function to work both on DOM
tree and composed tree with introducing member functions to strategy class
|VisibleSelection::InDOMTree|.

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=197320

[yosin_UTC9, 2015-06-18 04:36:35]

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

[yosin_UTC9, 2015-06-18 05:18:39]

PTAL

[tkent, 2015-06-18 05:36:41]

The CQ bit was checked by tkent@chromium.org

[tkent, 2015-06-18 05:36:41]

lgtm

[commit-bot: I haz the power, 2015-06-18 05:36:55]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1187973007/1

[commit-bot: I haz the power, 2015-06-18 05:57:19]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=197320