Avoid allocating temporary ranges in connection with text and character iterators.

30% performance improvement on DOM/textarea-edit on the oilpan build.
2% performance improvement on DOM/textarea-edit on the non-oilpan build.

R=yosin@chromium.org
BUG=388681

Review URL: https://codereview.chromium.org/544083002

git-svn-id: svn://svn.chromium.org/blink/trunk@181551 bbb929c8-8fbe-4397-9dbb-9b2b20218538