Capture: Serialize only the content of initialized attachments If a resource is marked MayNeedInit, then we don't serialize it but mark the data as not initialized. Bug: angleproject:6041 Change-Id: If3d3431a58848f7835692fe10b30fab68c901d8a Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2976657 Reviewed-by: Cody Northrop <cnorthrop@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Gert Wollny <gert.wollny@collabora.com>