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

This CL was uploaded by git cl split.

R=hbos@chromium.org

Bug: 177475
Change-Id: I9bf72aa8640eb2d566687d126e89b0d1c24f2606
Reviewed-on: https://chromium-review.googlesource.com/889729Reviewed-by: Henrik Boström <hbos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#532360}

third_party/WebKit/Source/modules/peerconnection/RTCDataChannel.cpp

@@ -342,10 +342,10 @@ bool RTCDataChannel::HasPendingActivity() const {
   switch (ready_state_) {
     case kReadyStateConnecting:
       has_valid_listeners |= HasEventListeners(EventTypeNames::open);
-    // fallthrough intended
+      FALLTHROUGH;
     case kReadyStateOpen:
       has_valid_listeners |= HasEventListeners(EventTypeNames::message);
-    // fallthrough intended
+      FALLTHROUGH;
     case kReadyStateClosing:
       has_valid_listeners |= HasEventListeners(EventTypeNames::error) ||
                              HasEventListeners(EventTypeNames::close);