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- This fixes that Android WebView did not default to NTLMv2
- This was changed already for all other platforms but it did not
  take effect on WebView.
- Sets the default value of ntlm_v2_enable_ to true in HttpAuthPreferences
- Previously the default was changed in flags, but it did not apply when
  a default HttpAuthPreferences was created, but no flags/features
  are overriden.

BUG=chromium:830542,chromium:22532
TEST=unittests

Change-Id: If660a9b5ab3a23735407468b30ee0f58aff5ce6c
Reviewed-on: https://chromium-review.googlesource.com/1030250
Commit-Queue: Zentaro Kavanagh <zentaro@chromium.org>
Reviewed-by: Asanka Herath <asanka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#554873}