QuicTransport: Minor cleanups to SendStream

Move web_transport_close_proxy.h from send_stream.h to the .cc file.
Remove the USING_GARBAGE_COLLECTED_MIXIN macro as SendStream has no
mixins.

BUG=1011392

Change-Id: I946781955ba068e396a82d37cb78b2248edbe699
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2032750Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Commit-Queue: Adam Rice <ricea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#738865}

third_party/blink/renderer/modules/webtransport/quic_transport.cc

@@ -26,6 +26,7 @@
 #include "third_party/blink/renderer/core/streams/writable_stream.h"
 #include "third_party/blink/renderer/core/typed_arrays/dom_typed_array.h"
 #include "third_party/blink/renderer/modules/webtransport/send_stream.h"
+#include "third_party/blink/renderer/modules/webtransport/web_transport_close_proxy.h"
 #include "third_party/blink/renderer/platform/bindings/exception_code.h"
 #include "third_party/blink/renderer/platform/bindings/exception_state.h"
 #include "third_party/blink/renderer/platform/bindings/script_state.h"

third_party/blink/renderer/modules/webtransport/send_stream.cc

@@ -7,6 +7,7 @@
 #include <utility>
 
 #include "third_party/blink/renderer/modules/webtransport/quic_transport.h"
+#include "third_party/blink/renderer/modules/webtransport/web_transport_close_proxy.h"
 #include "third_party/blink/renderer/platform/heap/visitor.h"
 
 namespace blink {

third_party/blink/renderer/modules/webtransport/send_stream.h

@@ -10,8 +10,6 @@
 #include "mojo/public/cpp/system/data_pipe.h"
 #include "third_party/blink/renderer/modules/modules_export.h"
 #include "third_party/blink/renderer/modules/webtransport/outgoing_stream.h"
-#include "third_party/blink/renderer/modules/webtransport/web_transport_close_proxy.h"
-#include "third_party/blink/renderer/platform/heap/garbage_collected.h"
 
 namespace blink {
 
@@ -20,7 +18,6 @@ class QuicTransport;
 
 class MODULES_EXPORT SendStream final : public OutgoingStream {
   DEFINE_WRAPPERTYPEINFO();
-  USING_GARBAGE_COLLECTED_MIXIN(SendStream);
 
  public:
   // SendStream doesn't have a JavaScript constructor. It is only constructed