Make Android HttpNegotiateAuthenticator work without an activity

Fallback on the various alternatives to
AccountManager#getAuthTokenByFeatures that don't require an
activity when we don't have one. This will allow using this
authenticator in WebView.

BUG=533513

Review URL: https://codereview.chromium.org/1422693002

Cr-Commit-Position: refs/heads/master@{#361871}
3 files changed