Update policy proto path for browser tests

This moved from policy/proto to components/policy/proto in https://codereview.chromium.org/2273783002 and this updates the Python server code to unbreak the test.

TBR=jianli@chromium.org

Review-Url: https://codereview.chromium.org/2286473003
Cr-Commit-Position: refs/heads/master@{#414628}
1 file changed