Checkout Polymer using bower instead of the raw repository.

third_party/polymer/PATENTS

-Additional IP Rights Grant (Patents)
-
-"This implementation" means the copyrightable works distributed by
-Google as part of the Polymer project.
-
-Google hereby grants to You a perpetual, worldwide, non-exclusive,
-no-charge, royalty-free, irrevocable (except as stated in this section)
-patent license to make, have made, use, offer to sell, sell, import,
-transfer and otherwise run, modify and propagate the contents of this
-implementation of Polymer, where such license applies only to those
-patent claims, both currently owned or controlled by Google and acquired
-in the future, licensable by Google that are necessarily infringed by
-this implementation of Polymer.  This grant does not include claims
-that would be infringed only as a consequence of further modification of
-this implementation.  If you or your agent or exclusive licensee
-institute or order or agree to the institution of patent litigation
-against any entity (including a cross-claim or counterclaim in a
-lawsuit) alleging that this implementation of Polymer or any code
-incorporated within this implementation of Polymer constitutes
-direct or contributory patent infringement, or inducement of patent
-infringement, then any patent rights granted to you under this License
-for this implementation of Polymer shall terminate as of the date
-such litigation is filed.