[WebGPU] Replace m_performWithMediaPlayerOnMainThread with the m_gpuConnectionToWebProcess as m_performWithMediaPlayerOnMainThread is not really needed
radar://115294252
Pull request: https://github.com/WebKit/WebKit/pull/17659
Committed 267874@main (bb19a861180a): <https://commits.webkit.org/267874@main> Reviewed commits have been landed. Closing PR #17659 and removing active labels.