qcow: Add raw file struct
qcow: Add raw file struct

The raw file struct will be used to hold enough state for basic
operations. This will allow mutating the file without taking a mutable
reference to an entire QcowFile.

Change-Id: Ia0a86537915da039274923df2f85c22d191b9969
Signed-off-by: Dylan Reid <c791bfe44996c1eed9c7149a0c5f12a86d58eb85@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1207450
Commit-Ready: ChromeOS CL Exonerator Bot <fa429e5907f00867f797423aea74327bb02c91b6@appspot.gserviceaccount.com>
Reviewed-by: Chirantan Ekbote <35787c0e27de5c48735e07f8324823b765e8bcbc@chromium.org>

google/crosvm,google/crosvm,google/crosvm,google/crosvm