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

This CL was uploaded by git cl split.

R=sadrul@chromium.org

Bug: 177475
Change-Id: I39e7b389e2bb228ca717c2029a7c34d2f32b6446
Reviewed-on: https://chromium-review.googlesource.com/890063
Commit-Queue: Nico Weber <thakis@chromium.org>
Commit-Queue: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Cr-Commit-Position: refs/heads/master@{#532180}

content/browser/renderer_host/input/touch_selection_controller_client_aura.cc

@@ -382,7 +382,7 @@ void TouchSelectionControllerClientAura::OnSelectionEvent(
   switch (event) {
     case ui::SELECTION_HANDLES_SHOWN:
       quick_menu_requested_ = true;
-      // Fall through.
+      FALLTHROUGH;
     case ui::INSERTION_HANDLE_SHOWN:
       UpdateQuickMenu();
       env_pre_target_handler_.reset(new EnvPreTargetHandler(