Enable "Always Open Files of This Type" even for dangerous file types. The

advanced user knows what they were doing, and dangerous file types will still
go through the warning dialog depending on user gesture level.

BUG=65895
TEST=download_manager_unittest.cc

Review URL: http://codereview.chromium.org/6196001

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@70853 0039d316-1c4b-4281-b951-d872f2087c98