Fix 45: Do not proxy requests for Widevine

[jumde]

Fix #45

Test Plan:

• With Browser

  • Navigate to https://bitmovin.com/demos/drm
  • Allow Widevine and verify the request for update is sent to update.googleapis.com
  • Ensure that the download is triggered from *.gvt1.com or *.dl.google.com

• With curl:

% curl -Ls -o /dev/null -w '%{url_effective}' -d '{"request":{"@os":"mac","@updater":"","acceptformat":"crx2,crx3","app":[{"appid":"oimompecagnajdejgnnjijobebaeigek","enabled":true,"installsource":"ondemand","ping":{"r":-2},"updatecheck":{},"version":"0.0.0.0"}],"arch":"x64","dedup":"cr","domainjoined":false,"hw":{"physmemory":16},"lang":"","nacl_arch":"x86-64","os":{"arch":"x86_64","platform":"Mac OS X","version":"10.15.5"},"prodchannel":"stable","prodversion":"83.1.12.20","protocol":"3.1","requestid":"{67dd796c-ac2d-46f9-a56d-6495e7c92640}","sessionid":"{fd35f289-fb9a-4a7c-8acf-9576b1d0c5eb}","updaterchannel":"stable","updaterversion":"83.1.12.20"}}' -H "Content-Type: application/json" -X POST http://localhost:8192/extensions
https://update.googleapis.com/service/update2/json

[kjozwiak]

Went through QA via brave/brave-core#5846 (comment).