Make Libcore.rawOs final.

No code currently seems to rely on updating this static field (not even
in tests), and there's no obvious reason why anyone should be able to.

This CL makes the field final.

Bug: 115503977
Test: Treehugger
Change-Id: I4b00e0a2379def811deb38049df3d1331ce3e508
1 file changed