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

This CL was uploaded by git cl split.

R=mfoltz@chromium.org

Bug: 177475
Change-Id: Ie99aa136b2a0d27de3e24ae1e9b737edd0c6e875
Reviewed-on: https://chromium-review.googlesource.com/891921Reviewed-by: mark a. foltz <mfoltz@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#532671}

chrome/browser/ui/webui/media_router/media_router_file_dialog.cc

@@ -252,6 +252,7 @@ IssueInfo MediaRouterFileDialog::CreateIssue(
       // Create issue shouldn't be called with FILE_OK, but to ensure things
       // compile, fall through sets |issue_title| to the generic error.
       NOTREACHED();
+      FALLTHROUGH;
     case MediaRouterFileDialog::UNKNOWN_FAILURE:
       issue_title = l10n_util::GetStringUTF8(
           IDS_MEDIA_ROUTER_ISSUE_FILE_CAST_GENERIC_ERROR);