See http://crbug.com/417850 for UTF-32
See http://bugs.icu-project.org/trac/ticket/12147 for C4275 warning
from MSVC.

BUG=575007
TEST=Layout tests fast/encoding/*
TEST=MSVC does not emit C4275 warning any more
R=jsbell@chromium.org

Review URL: https://codereview.chromium.org/1664293002 .