Introduce a delegate to avoid hardcoding "chrome-extension" in net/.

Also, deal with a couple of TODOs in the throttling code, and remove
metrics we no longer need since we are no longer running field trials
for this code.

BUG=119760


Review URL: https://chromiumcodereview.appspot.com/10440119

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@141000 0039d316-1c4b-4281-b951-d872f2087c98
21 files changed