[Sync] Remove bookmark model observer on DTC abort

If the bookmark datatype controller gets aborted, but the bookmark model
then finishes loading, we crash due to resetting the model load callback
upon abort. At abort time, we should instead unregister from all model
callbacks.

(Relanding r248259 with crash fix. Original review at
https://codereview.chromium.org/138543009/)

BUG=333948

Review URL: https://codereview.chromium.org/141473005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249436 0039d316-1c4b-4281-b951-d872f2087c98
Some more non-Aura Windows cleanup.

BUG=330735

Review URL: https://codereview.chromium.org/142393003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249437 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 249437
Updates the URL for verified access learn more link.

BUG=340840
R=dkrahn@chromium.org, oshima@chromium.org

Review URL: https://codereview.chromium.org/154643003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249438 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 249438