Update ANativeWindow_getNextFrameId docs to specify API contract

We rely on frame ids starting at 1, with 0 being invalid/uninitialize, and incrementing for each frame chronologically for as long as the underlying surface doesn't change.

Test: N/A
Change-Id: I90e9593b7ae852bcc90c5c17bc4969c7d827b2d9
1 file changed