Work more on getting things built with -Wimplicit-fallthrough.

This CL was uploaded by git cl split.

R=zhenw@chromium.org

Bug: 177475
Change-Id: I87d874d14490cd2476ef10f7b0aeaa058aa9273f
Reviewed-on: https://chromium-review.googlesource.com/889961Reviewed-by: Charlie Andrews <charliea@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#532959}

tools/battor_agent/battor_agent.cc

@@ -435,6 +435,7 @@ void BattOrAgent::PerformAction(Action action) {
       // Clear stored samples from prior attempts to read sample frames.
       samples_.clear();
       calibration_frame_.clear();
+      FALLTHROUGH;
     case Action::READ_DATA_FRAME:
       // The first frame sent back from the BattOr contains voltage and current
       // data that excludes whatever device is being measured from the