Elide proxy authentication headers

The change prevent the data reduction proxy's authentication
headers from being exposed in net logs and dev tools.

BUG=179382

Review URL: https://codereview.chromium.org/149703005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248566 0039d316-1c4b-4281-b951-d872f2087c98
Disable Flaky ExtensionBrowserTest.RSSParseFeedValidFeed1.

Recent flake:
http://build.chromium.org/p/chromium.win/builders/Win7%20Tests%20%28dbg%29%286%29/builds/25174

Flakiness dashboard:
http://chromium-build-logs.appspot.com/gtest_query?gtest_query=ExtensionBrowserTest.RSSParseFeedValidFeed1

BUG=340354
TEST=none
R=erg@chromium.org
TBR=finnur@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/150693004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248567 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248566
SVN changes up to revision 248567