Add two small features to the HttpCache for benchmarking/debugging.

The first exposes a method to close all idle sockets.  This allows
me to create benchmark tests in the app which can close
connections before starting the test for better simulations.

The second change is to expose cache modes for cache
disabled and cache bypassed.  DISABLE sets the LOAD_DISABLE_CACHE
on every request; BYPASS sets the LOAD_BYPASS_CACHE on 
every request.

TEST=http_cache_unittest.cc
BUG=6754

Review URL: http://codereview.chromium.org/119189

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@17720 0039d316-1c4b-4281-b951-d872f2087c98
3 files changed