HttpAuthHandlerDigest unit test cleanup.
HttpAuthHandlerDigest unit test cleanup.

DCHECK replaced by EXPECT for HttpAuthHandlerDigest unittests.

Also, changed RespondToChallenge to return a success boolean and LOG the failure reasons, rather than returning an error string. 

BUG=None
TEST=net_unittests --gtest_filter="*HttpAuthHandlerDigest*"
Review URL: http://codereview.chromium.org/5205005

git-svn-id: dd90618784b6a4b323ea0c23a071cb1c9e6f2ac7@68006 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser