Fix Destruction inside WGC Callback

If we are notified of the destruction of the window before a
CaptureFrame call can fail, then we may end up attempting to destroy the
underlying WGC object inside it's own event handler. This can be
problematic, as the class itself may want to run other code. Instead,
we just unsubscribe and signal that any future CaptureFrame calls should
reject.

This also removes setting "is_capture_started_=false" in the item closed
handler, as all that served to do is cause the WgcCapturerWin code to
attempt to restart the capturer, and somewhat muddies up our metrics.

Bug: chromium:1413005
Change-Id: Ibccb7a2e7ce531ba80b4b331b9bc2cda0ff75f4e
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/292762
Auto-Submit: Alexander Cooper <alcooper@chromium.org>
Reviewed-by: Mark Foltz <mfoltz@chromium.org>
Commit-Queue: Mark Foltz <mfoltz@chromium.org>
Commit-Queue: Alexander Cooper <alcooper@chromium.org>
Cr-Commit-Position: refs/heads/main@{#39275}

modules/desktop_capture/win/wgc_capture_session.cc

@@ -397,17 +397,14 @@ HRESULT WgcCaptureSession::OnItemClosed(WGC::IGraphicsCaptureItem* sender,
 
   RTC_LOG(LS_INFO) << "Capture target has been closed.";
   item_closed_ = true;
-  is_capture_started_ = false;
 
   RemoveEventHandlers();
 
-  mapped_texture_ = nullptr;
-  session_ = nullptr;
-  frame_pool_ = nullptr;
-  direct3d_device_ = nullptr;
-  item_ = nullptr;
-  d3d11_device_ = nullptr;
-
+  // Do not attempt to free resources in the OnItemClosed handler, as this
+  // causes a race where we try to delete the item that is calling us. Removing
+  // the event handlers and setting `item_closed_` above is sufficient to ensure
+  // that the resources are no longer used, and the next time the capturer tries
+  // to get a frame, we will report a permanent failure and be destroyed.
   return S_OK;
 }