Fix DownloadManager crash when DownloadManagerDelegate isn't set

BUG=

Review URL: https://codereview.chromium.org/100753003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238896 0039d316-1c4b-4281-b951-d872f2087c98
Add Finch experiment for new-user-management.

BUG=324046

Review URL: https://codereview.chromium.org/105573002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238897 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238897