Handle redirects in AuthenticatingURLLoaderImpl.

Handle redirects in AuthenticatingURLLoaderImpl.

This CL adds |FollowRedirect()| to authenticating_url_loader.mojom. The logic
for implementing redirects is as follows:

- When the AuthenticatingURLLoaderImpl receives a response that is a redirect,
  it sets the redirect url as the url of its "new" request and clears its
  authentication state, since that authentication state was for the
  pre-redirect request. If the client had requested that requests be
  automatically followed, it then calls |FollowRedirect()| on its internal
  URLLoader. Otherwise, it returns the response to the client but saves its
  internal URLLoader in case the client responds by calling |FollowRedirect()|.

R=qsr@chromium.org

Committed: https://chromium.googlesource.com/external/mojo/+/524ef56969655b5eff8becc6ca737cc2663d156d

[blundell, 2015-05-27 13:27:20]

blundell@chromium.org changed reviewers:
+ qsr@chromium.org

[qsr, 2015-05-27 14:29:36]

lgtm

https://codereview.chromium.org/1146923003/diff/20001/services/authenticating...
File services/authenticating_url_loader/authenticating_url_loader_impl.cc
(right):

https://codereview.chromium.org/1146923003/diff/20001/services/authenticating...
services/authenticating_url_loader/authenticating_url_loader_impl.cc:51:
DCHECK(!auto_follow_redirects_);
You should not dcheck on a wrong usage of your API. Just return a null response.

[blundell, 2015-05-27 15:58:18]

Patchset #3 (id:40001) has been deleted

[blundell, 2015-05-27 16:01:43]

Committed patchset #3 (id:60001) manually as
524ef56969655b5eff8becc6ca737cc2663d156d (presubmit successful).

[blundell, 2015-06-03 10:55:11]

https://codereview.chromium.org/1146923003/diff/20001/services/authenticating...
File services/authenticating_url_loader/authenticating_url_loader_impl.cc
(right):

https://codereview.chromium.org/1146923003/diff/20001/services/authenticating...
services/authenticating_url_loader/authenticating_url_loader_impl.cc:51:
DCHECK(!auto_follow_redirects_);
On 2015/05/27 14:29:36, qsr wrote:
> You should not dcheck on a wrong usage of your API. Just return a null
response.

Done.