Camera: Document 3.4 metadata selection logic.

Bug: 119575429
Test: Ensure everything still builds.
Change-Id: I6500ab06b8c392310009ecfa0570000742fd069c
Merged-In: I6500ab06b8c392310009ecfa0570000742fd069c
(cherry picked from commit a5cbabbee988b4cfc4c3d45106220b296f7c3a38)
2 files changed