The purpose of the CL is to enable re-use of the mmap support in dart2js
in other tools (e.g. package:heapsnapshot & package:kernel).
There's a small refactoring to remove zero-termination logic out of the
general mmap support.
Change-Id: I7a9889acea43d5ce0ab1eb10dcefbfa74c44bf93
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/279348
Reviewed-by: Jens Johansen <jensj@google.com>
Reviewed-by: Nate Biggs <natebiggs@google.com>
Commit-Queue: Martin Kustermann <kustermann@google.com>
