Fix implicit-fallthrough warnings. DO NOT MERGE.

These changes are not needed in goog/master.

Test: make checkbuild
Bug: 112564944
Change-Id: I4f1727d9b33108d34d314787460aa1d2298ae5b2
(cherry picked from commit c5def0beebeccb24da85f71d58f77e18cdb5f9ed)
Exempt-From-Owner-Approval: do not block on new warnings
1 file changed