For more info, see
http://dev.chromium.org/developers/testing/undefinedbehaviorsanitizer

TESTED=Passing compilation using:
GYP_DEFINES="ubsan=1"
GYP_DEFINES="ubsan_vptr=1"

R=harryjin@google.com, pbos@webrtc.org
BUG=libyuv:563,webrtc:5124

Review URL: https://codereview.chromium.org/1659713002 .