This CL has DrawingBuffer pass the ClientSharedImage via which it
creates its TransferableResource in ExportCanvasResource() to
ExternalCanvasResource as a step to having ExternalCanvasResource always
have ClientSharedImage internally.

Note: This theoretically has the possibility of extending the lifetime
of the SharedImage. However, in practice the SharedImage will already
be being kept alive until the TransferableResource releases it [1].

[1] https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/platform/graphics/gpu/drawing_buffer.cc;l=636-637;drc=1e9882b63079c84a1f7af3460aca17ae920edb08?q=drawing_buffer.cc&ss=chromium

Bug: 353744937
Change-Id: I1ce1225cd4220ed0c7e5cd10257cf4fa74601e0a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5724368


Commit-Queue: Colin Blundell <blundell@chromium.org>
Reviewed-by: Vasiliy Telezhnikov <vasilyt@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1330231}
NOKEYCHECK=True
GitOrigin-RevId: 31876b69362e69c88f54b4329e612b1fa3a2ef7e