Better match IE's proxy settings.

 * When BOTH autodetect and custom PAC script are given, try both.
 * Use successful PAC parsing as the heuristic for determining when a script   is valid (rather than first-request). 
 * Only apply the proxy bypass list when using non-PAC.

The high level explanation on how this works:

http://sites.google.com/a/chromium.org/dev/developers/design-documents/proxy-settings-fallback

BUG= http://crbug.com/18271, http://crbug.com/9985
TEST=unit tests.
Review URL: http://codereview.chromium.org/160510

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@22430 0039d316-1c4b-4281-b951-d872f2087c98
22 files changed