Remaining changes to build all code in src.git with -Wimplicit-fallthrough.

This CL was uploaded by git cl split.

R=treib@chromium.org

Bug: 177475
Change-Id: I0bda56f41b13861fec0c2b0ffb604fce759d35f8
Reviewed-on: https://chromium-review.googlesource.com/891878Reviewed-by: Marc Treib <treib@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#532844}

chrome/browser/supervised_user/supervised_user_navigation_throttle.cc

@@ -79,6 +79,7 @@ int GetHistogramValueForFilteringBehavior(
           // Should never happen, only used for requests from Webview
           NOTREACHED();
       }
+      FALLTHROUGH;
     case SupervisedUserURLFilter::INVALID:
       NOTREACHED();
   }