cros: Use webview.addContentScripts for new Gaia SAML.

cros: Use webview.addContentScripts for new Gaia SAML.

- Use webview.addContentScripts to to inject js;
- Enable crendential passing tests;
- Make the test listen for authFlowChange event only when needed
  because it is fired on every auth page load now to correctly
  propagate the auth domain change;

BUG=467068
Committed: https://crrev.com/af7b6fb09cfc4eb8591901b7442c4bf5f5af800d
Cr-Commit-Position: refs/heads/master@{#327114}

[xiyuan, 2015-04-06 23:17:24]

xiyuan@chromium.org changed reviewers:
+ dzhioev@chromium.org

[xiyuan, 2015-04-06 23:17:25]

Sent out for early review.

Note it depends on https://codereview.chromium.org/1056533002/ (API CL and
incognito fix https://codereview.chromium.org/1056133005/)

[dzhioev (left Google), 2015-04-07 14:31:34]

dzhioev@chromium.org changed reviewers:
+ dpolukhin@chromium.org

[dzhioev (left Google), 2015-04-07 14:32:14]

LGTM

+Dmitry for saml_browsertest.cc review.

[Dmitry Polukhin, 2015-04-07 14:39:23]

LGTM SAML test but this CL will have merge conflicts with
https://codereview.chromium.org/1054403002

[xiyuan, 2015-04-27 17:27:27]

Almost there. The last piece this CL depends on is
https://codereview.chromium.org/1062963006/ (make AddContentScript work for
incognito profile). I will land after that CL is in.

[xiyuan, 2015-04-27 19:33:53]

The CQ bit was checked by xiyuan@chromium.org

[xiyuan, 2015-04-27 19:33:54]

The patchset sent to the CQ was uploaded after l-g-t-m from
dpolukhin@chromium.org, dzhioev@chromium.org
Link to the patchset: https://codereview.chromium.org/1066573003/#ps100001
(title: "rebase")

[commit-bot: I haz the power, 2015-04-27 19:34:34]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1066573003/100001

[commit-bot: I haz the power, 2015-04-27 20:19:57]

Committed patchset #6 (id:100001)

[commit-bot: I haz the power, 2015-04-27 20:20:50]

Patchset 6 (id:??) landed as
https://crrev.com/af7b6fb09cfc4eb8591901b7442c4bf5f5af800d
Cr-Commit-Position: refs/heads/master@{#327114}