Allow PpapiHostMsg_FlashDRM_Create with private permission.

This is a follow up CL of: https://chromiumcodereview.appspot.com/21732003

FlashDRM is the backend of both Flash_DeviceID and Flash_DRM interfaces. Since
Flash_DeviceID requires private permission and Flash_DRM requires flash
permission. We should allow PpapiHostMsg_FlashDRM_Create handling with either of
these permissions.

BUG=310912
R=raymes@google.com
TBR=raymes@chromium.org
TEST=Device ID works with private permission.

Review URL: https://codereview.chromium.org/38593004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230644 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230644