mojo heap migration: FileReaderLoader exception

Mojo objects are being moved to the heap allow them to be managed by
Oilpan. This class needs to be converted to GarbageCollected first.
Leave a TODO() to update receiver_.

Bug: 937038, 1049056
Change-Id: I9b68f6e2a5f7953cbd1309345097fde1c2191039
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2096066Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Commit-Queue: Johann Koenig <johannkoenig@google.com>
Cr-Commit-Position: refs/heads/master@{#752724}

third_party/blink/renderer/core/fileapi/file_reader_loader.h

@@ -173,6 +173,9 @@ class CORE_EXPORT FileReaderLoader : public mojom::blink::BlobReaderClient {
 
   mojo::ScopedDataPipeConsumerHandle consumer_handle_;
   mojo::SimpleWatcher handle_watcher_;
+  // TODO(crbug.com/937038, crbug.com/1049056): Make FileReaderLoaderClient
+  // GarbageCollected. It will then be possible to use the HeapMojoReceiver
+  // wrapper for receiver_.
   mojo::Receiver<mojom::blink::BlobReaderClient> receiver_{this};
   bool received_all_data_ = false;
   bool received_on_complete_ = false;