2nd reland of "[Cast MRP] Stop mirroring immediately when a the tab is closed."

This is a reland of f51b93d7

Original change's description:
> [Cast MRP] Stop mirroring immediately when a the tab is closed.
>
> Bug: 1095764, b/159154368
> Change-Id: I36829467e3a6477499c76ae0b15e110acba00c89
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2346911
> Reviewed-by: Yuri Wiitala <miu@chromium.org>
> Commit-Queue: John Williams <jrw@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#803343}

Bug: 1095764
Bug: b/159154368
Change-Id: I9d01af31895152afbf13a21b00091f12352131a3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2402181
Commit-Queue: John Williams <jrw@chromium.org>
Reviewed-by: mark a. foltz <mfoltz@chromium.org>
Reviewed-by: Yuri Wiitala <miu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#812518}

components/mirroring/service/mirroring_service.cc

@@ -15,7 +15,10 @@ MirroringService::MirroringService(
     mojo::PendingReceiver<mojom::MirroringService> receiver,
     scoped_refptr<base::SingleThreadTaskRunner> io_task_runner)
     : receiver_(this, std::move(receiver)),
-      io_task_runner_(std::move(io_task_runner)) {}
+      io_task_runner_(std::move(io_task_runner)) {
+  receiver_.set_disconnect_handler(
+      base::BindOnce(&MirroringService::OnDisconnect, base::Unretained(this)));
+}
 
 MirroringService::~MirroringService() = default;
 
@@ -33,4 +36,8 @@ void MirroringService::Start(
       std::move(inbound_channel), io_task_runner_);
 }
 
+void MirroringService::OnDisconnect() {
+  session_.reset();
+}
+
 }  // namespace mirroring

components/mirroring/service/mirroring_service.h

@@ -33,6 +33,8 @@ class COMPONENT_EXPORT(MIRRORING_SERVICE) MirroringService final
              mojo::PendingReceiver<mojom::CastMessageChannel> inbound_channel)
       override;
 
+  void OnDisconnect();
+
   mojo::Receiver<mojom::MirroringService> receiver_;
   const scoped_refptr<base::SingleThreadTaskRunner> io_task_runner_;
   std::unique_ptr<Session> session_;  // Current mirroring session.