This struct matches the layout defined by Microsoft and replaces
Breakpad's MDRawContextARM64_Old. This CL updates the processor to
understand either the old or new structs, but clients continue to write
the old structs.
Change-Id: I8dedd9ddb2ec083b802723b9ac87beb18d98edbd
Reviewed-on: https://chromium-review.googlesource.com/1155938
Reviewed-by: Mark Mentovai <mark@chromium.org>
