Prepare ios code for building with -Wimplicit-fallthrough.

No behavior change.

Actually turning on the warning is blocked on an issue in protobuf
(see crbug.com/809157), so this will happen in a future CL.

Bug: 177475
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: If4a2e661257a77298bacf589b7bdf02e0e54374d
Reviewed-on: https://chromium-review.googlesource.com/902066Reviewed-by: David Roger <droger@chromium.org>
Reviewed-by: Lambros Lambrou <lambroslambrou@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#534862}

ios/chrome/browser/ui/payments/payment_request_error_view_controller.mm

@@ -115,6 +115,7 @@ typedef NS_ENUM(NSInteger, ItemType) {
       PaymentsTextCell* messageCell =
           base::mac::ObjCCastStrict<PaymentsTextCell>(cell);
       messageCell.textLabel.textColor = [[MDCPalette greyPalette] tint600];
+      break;
     }
     default:
       break;

ios/net/crn_http_protocol_handler.mm

@@ -630,6 +630,7 @@ void HttpProtocolHandlerCore::SetLoadFlags() {
     switch ([request_ cachePolicy]) {
       case NSURLRequestReloadIgnoringLocalAndRemoteCacheData:
         load_flags |= LOAD_BYPASS_CACHE;
+        FALLTHROUGH;
       case NSURLRequestReloadIgnoringLocalCacheData:
         load_flags |= LOAD_DISABLE_CACHE;
         break;

remoting/ios/audio/audio_player_ios.mm

@@ -148,7 +148,7 @@ void AudioPlayerIos::StartOnAudioThread() {
       GenerateOutputQueue((void*)this);
       GenerateOutputBuffers(audio_frame_supplier_->bytes_per_frame());
       state_ = STOPPED;
-    // Fall-through intended.
+      FALLTHROUGH;
     case STOPPED:
       PrimeQueue();
       return;