Don't fail on ID overlap for 0th offset when 'offset' attribute is used.
Don't fail on ID overlap for 0th offset when 'offset' attribute is used.

TBR=benrg@chromium.org
BUG=none

Review URL: https://chromiumcodereview.appspot.com/11742040
megamanfx/grit-i18n,qjw/grit-i18n,skidzen/grit-i18n,korusdipl/grit-i18n,joisig/grit-i18n,willbittner/grit-i18n,metasmile/grit-i18n,megamanfx/grit-i18n,invalidstatement/grit-i18n,CrankWheel/grit-i18n,willbittner/grit-i18n,lhopps/grit-i18n,qjw/grit-i18n,sevansahumIlovemuhammad/grit-i18n,korusdipl/grit-i18n,joisig/grit-i18n,sevansahumIlovemuhammad/grit-i18n,skidzen/grit-i18n,lhopps/grit-i18n,metasmile/grit-i18n,invalidstatement/grit-i18n