[fuchsia] Fix BlinkMessageFromFidl() to handle |incoming_transfer|.

FidlMessageFromBlink() populates the |incoming_transfer| field of the
resulting fuchsia.web.Message with any |ports|, but the
BlinkMessageFromFidl() API only considered |outgoing_transfer|. Round-
trip messages between the two would therefore drop any associated ports.

Bug: b/154200695
Change-Id: Ib5b2346d321219166b62d5b60473852a7ffd9d61
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2362589
Auto-Submit: Wez <wez@chromium.org>
Commit-Queue: Kevin Marshall <kmarshall@chromium.org>
Reviewed-by: Kevin Marshall <kmarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#799203}

fuchsia/base/message_port.cc

@@ -38,10 +38,17 @@ base::Optional<fuchsia::web::FrameError> BlinkMessageFromFidl(
   blink_message->data = data_utf16;
 
   if (fidl_message.has_outgoing_transfer()) {
-    for (fuchsia::web::OutgoingTransferable& outgoing :
+    for (fuchsia::web::OutgoingTransferable& transferrable :
          *fidl_message.mutable_outgoing_transfer()) {
       blink_message->ports.push_back(
-          BlinkMessagePortFromFidl(std::move(outgoing.message_port())));
+          BlinkMessagePortFromFidl(std::move(transferrable.message_port())));
+    }
+  }
+  if (fidl_message.has_incoming_transfer()) {
+    for (fuchsia::web::IncomingTransferable& transferrable :
+         *fidl_message.mutable_incoming_transfer()) {
+      blink_message->ports.push_back(
+          BlinkMessagePortFromFidl(std::move(transferrable.message_port())));
     }
   }