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

This CL was uploaded by git cl split.

R=dtapuska@chromium.org

Bug: 177475
Change-Id: I78e1026f86a8defe0fb7fb3683dd288f7b376dcd
Reviewed-on: https://chromium-review.googlesource.com/889734Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#532218}

ui/events/blink/input_handler_proxy.cc

@@ -299,6 +299,7 @@ void InputHandlerProxy::DispatchSingleInputEvent(
   switch (event_with_callback->event().GetType()) {
     case blink::WebGestureEvent::kGestureScrollBegin:
       is_first_gesture_scroll_update_ = true;
+      FALLTHROUGH;
     case blink::WebGestureEvent::kGestureFlingStart:
     case blink::WebGestureEvent::kGesturePinchBegin:
     case blink::WebGestureEvent::kGestureScrollUpdate: