GitLab

Copy FrameSelection.{cpp,h} to SelectionEditor.{cpp,h}

This patch copies "FrameSelection.{cpp,h}" to "SelectionEditor.{cpp,h}" as
a preparation of moving |FrameSelection::modify()| to |SelectionEditor| class
for inheriting change history.

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
NOTRY=true

Review URL: https://codereview.chromium.org/1331543002

git-svn-id: svn://svn.chromium.org/blink/trunk@201858 bbb929c8-8fbe-4397-9dbb-9b2b20218538