Add Dart MIME type to mimeTypeAllowedByNosniff

BUG=

Review URL: https://codereview.chromium.org/1661043004 .

git-svn-id: https://src.chromium.org/blink/branches/dart/2454_1@202767 bbb929c8-8fbe-4397-9dbb-9b2b20218538
1 file changed