Fix OMA download through context menu

Fix OMA download through context menu

For OMA downloads, chrome doesn't handle it correctly as the file needs to be converted to a .fl file and encrypted on the device.
The android DownloadManager provides such covertion.
As a result, we need to provide a way for us to intercept certain OMA downloads

BUG=382698
Committed: https://crrev.com/b44a546b94b78eee2d05f0e58aaf18bc63f97977
Cr-Commit-Position: refs/heads/master@{#294676}

[qinmin, 2014-09-12 19:38:09]

qinmin@chromium.org changed reviewers:
+ tedchoc@chromium.org

[qinmin, 2014-09-12 19:38:10]

PTAL

[Ted C, 2014-09-12 20:23:43]

lgtm

[qinmin, 2014-09-12 21:01:07]

The CQ bit was checked by qinmin@chromium.org

[commit-bot: I haz the power, 2014-09-12 21:02:18]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/571613002/1

[commit-bot: I haz the power, 2014-09-12 22:08:03]

Committed patchset #1 (id:1) as 9989059450109ab3a9f00cbc361c60754935e223

[commit-bot: I haz the power, 2014-09-12 22:12:40]

Patchset 1 (id:??) landed as
https://crrev.com/b44a546b94b78eee2d05f0e58aaf18bc63f97977
Cr-Commit-Position: refs/heads/master@{#294676}