Push mapping from file extension to GID.

An upcoming sdcardfs change will offer to automatically change the
GID of files on external storage based on the extension, but we need
to tell the kernel the mapping that we'd like to see.

Test: build, boots
Bug: 34733702
Change-Id: I15d4db5423d18c4da17e198c0e45a8adb381fed2
2 files changed