gamepad: convert GamepadSharedMemoryReader to GC

Make the class GarbageCollected so that the mojo::Re{mote,ceiver}
objects can be managed as well.

Change-Id: I7d0919d900eb54c557cceda07e496bd4920b2b42
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2106989Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>
Commit-Queue: Johann Koenig <johannkoenig@google.com>
Cr-Commit-Position: refs/heads/master@{#751955}

third_party/blink/renderer/modules/gamepad/gamepad_dispatcher.cc

@@ -53,6 +53,7 @@ void GamepadDispatcher::InitializeHaptics() {
 }
 
 void GamepadDispatcher::Trace(Visitor* visitor) {
+  visitor->Trace(reader_);
   PlatformEventDispatcher::Trace(visitor);
 }
 
@@ -85,7 +86,7 @@ void GamepadDispatcher::DispatchDidConnectOrDisconnectGamepad(
 void GamepadDispatcher::StartListening(LocalFrame* frame) {
   if (!reader_) {
     DCHECK(frame);
-    reader_ = std::make_unique<GamepadSharedMemoryReader>(*frame);
+    reader_ = MakeGarbageCollected<GamepadSharedMemoryReader>(*frame);
   }
   reader_->Start(this);
 }

third_party/blink/renderer/modules/gamepad/gamepad_dispatcher.h

@@ -62,7 +62,7 @@ class GamepadDispatcher final : public GarbageCollected<GamepadDispatcher>,
                                              bool connected);
 
   scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
-  std::unique_ptr<GamepadSharedMemoryReader> reader_;
+  Member<GamepadSharedMemoryReader> reader_;
   mojo::Remote<device::mojom::blink::GamepadHapticsManager>
       gamepad_haptics_manager_remote_;
 };

third_party/blink/renderer/modules/gamepad/gamepad_shared_memory_reader.cc

@@ -25,6 +25,8 @@ GamepadSharedMemoryReader::GamepadSharedMemoryReader(LocalFrame& frame) {
       receiver_.BindNewPipeAndPassRemote(task_runner));
 }
 
+void GamepadSharedMemoryReader::Trace(Visitor* visitor) {}
+
 void GamepadSharedMemoryReader::SendStartMessage() {
   if (gamepad_monitor_remote_) {
     gamepad_monitor_remote_->GamepadStartPolling(

third_party/blink/renderer/modules/gamepad/gamepad_shared_memory_reader.h

@@ -13,6 +13,7 @@
 #include "mojo/public/cpp/bindings/receiver.h"
 #include "mojo/public/cpp/bindings/remote.h"
 #include "mojo/public/cpp/system/buffer.h"
+#include "third_party/blink/renderer/platform/heap/handle.h"
 
 namespace base {
 class ReadOnlySharedMemoryRegion;
@@ -28,10 +29,13 @@ namespace blink {
 class GamepadListener;
 class LocalFrame;
 
-class GamepadSharedMemoryReader : public device::mojom::blink::GamepadObserver {
+class GamepadSharedMemoryReader
+    : public GarbageCollected<GamepadSharedMemoryReader>,
+      public device::mojom::blink::GamepadObserver {
  public:
   explicit GamepadSharedMemoryReader(LocalFrame& frame);
   ~GamepadSharedMemoryReader() override;
+  void Trace(Visitor*);
 
   void SampleGamepads(device::Gamepads& gamepads);
   void Start(blink::GamepadListener* listener);