WebNN: Cache D3D shared fence handle in D3DImageBacking Avoid redundant OpenSharedHandle calls in EndAccessDawnBuffer by caching the last used D3DSharedFence. This persists the NT handle on the backing, reducing CPU overhead during frequent buffer access cycles in WebNN. Bug: 345352987 Change-Id: Id791de1e753d59086c811979c5addf8f0f92e07d Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7670172 Commit-Queue: Bernhart, Bryan <[email protected]> Reviewed-by: Vasiliy Telezhnikov <[email protected]> Cr-Commit-Position: refs/heads/main@{#1601411} NOKEYCHECK=True GitOrigin-RevId: a82e897fe39c0e334ae6816a30218eb8fbfcf87c