Fix an issue that android Download Manager doesn't handle OMA files correctly
For OMA files, it looks like that android download manager cannot correctly download it.
Some of the files cannot be downloaded, and some of the files downloaded has different binary content as the ones downloaed on chrome desktop.
Bypass android download manager for OMA mime types.
BUG=382698
Review URL: https://codereview.chromium.org/
331143010
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@282243 0039d316-1c4b-4281-b951-d872f2087c98