[...] You hereby grant to Google and to recipients of software distributed by Google a [...] patent license [to use and distribute] the Work, where such license applies only to those patent claims licensable by You that are necessarily infringed by Your Contribution(s) alone or by combination of Your Contribution(s) with the Work to which such Contribution(s) was submitted.
https://cla.developers.google.com/about/google-individual?cs...
You represent that Your Contribution submissions include complete details of any third-party license or other restriction (including, but not limited to, related patents and trademarks) of which you are personally aware and which are associated with any part of Your Contributions.
It doesn't require you to know if your code infringes patents, it just requires that IF you know, you disclose it.
Patents are a tool of harassing others for big companies. The only thing that is important is will a big company sue you or not.