Did the actions of Garner contribute to his death? Yes.
Did the actions of Brown contribute to his death? Yes
Did the actions of Trayvon contribute to his death? Yes.
It is true that Garner's actions contributed to his death -- but unless you are an anti-smoking Nazi, his actions weren't putting anyone in danger. He was violating a pretty scurrilous, and petty, ordinance. Yes, as some others have noted - his being out of shape probably contributed to his death, but he wasn't doing anything that required someone to rough him up.
Sometimes the cops are the bad guys and cause unnecessary deaths for misdemeanor offences. Those cops should be raked over the coals until such time as the bad ones, who have no value for human life (even those who commit some offences) are weeded out so they can pursue their own criminal lifestyles for the outside rather than the inside.