Fix one reaming style error in core/editing/TextIterator.cpp

This patch fixes one reaming from r160312 style error in  core/editing/TextIterator.cpp.

BUG=n/a
TEST=n/a; no behavior chagnes
R=morrita@chromium.org

Review URL: https://codereview.chromium.org/36633002

git-svn-id: svn://svn.chromium.org/blink/trunk@160315 bbb929c8-8fbe-4397-9dbb-9b2b20218538