Fix accidental implicit fallthroughs

-Wimplicit-fallthrough was printing warnings for these, they look
like real errors.  Fix them and re-enable the error.

Bug: 144040966
Test: treehugger
Merged-In: I818e18a995760f17b85b4c72ee577e531fa2a601
Change-Id: I818e18a995760f17b85b4c72ee577e531fa2a601
(cherry picked from commit fbeb4fc1397c0a193615c30c4ffc1c029b7ad69a)