Let the analyzer tell you if you've failed to override these methods by making them abstract instead of having them default to assert(false) or zero.
Let the analyzer tell you if you've failed to override these methods by making them abstract instead of having them default to assert(false) or zero.

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1235813006 .

afandria/mojo,jianglu/mojo,afandria/mojo,jianglu/mojo,afandria/mojo,jianglu/mojo,jianglu/mojo,jianglu/mojo,afandria/mojo,jianglu/mojo,afandria/mojo,jianglu/mojo,jianglu/mojo,afandria/mojo,afandria/mojo,afandria/mojo