Merge a bidi fix to ICU's M42 branch

The following two changes are cherry-picked along with the corresponding
patch file (bidi.patch) and update for README.chromium.

http://crrev.com/7c81740601355556e630da515b74d889ba2f8d08/source/common/ubidi.c
http://crrev.com/7c81740601355556e630da515b74d889ba2f8d08/source/common/ubidiimp.h

DEPS in M42 will be updated to include this change.

BUG=451799
TEST=none
TBR=inferno@chromium.org

Review URL: https://codereview.chromium.org/1004743003
4 files changed