Make LayoutSelection::SetSelection() local

Update member |paint_range| at Commit().
This CL also moves enum SelectionPaintInvalidationMode to local and
 renames it appropriately.

BUG=708453
TEST=No change in behavior

Review-Url: https://codereview.chromium.org/2906273002
Cr-Commit-Position: refs/heads/master@{#475478}
2 files changed