Utilize VisibleSelectionTemplate template class in SelectionController

This patch utilizes |VisibleSelectionTemplate| template class in
|SelectionController| class as replacement of |VisibleSelection::InDOMTree| and
|VisibleSelection::InComposedTree| for a preparation of full version of
|VisibleSelectionTemplate|.

This patch is a preparation of making selection to handle granularity for web
component, http://crrev.com/1363873004

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

Review URL: https://codereview.chromium.org/1371003002

Cr-Commit-Position: refs/heads/master@{#351039}
4 files changed