Processed file size not captured when copying from stdin

This is confusing as there is data uploaded to the object but the output shows zero.

Example:
```
$ echo test | gsutil cp - gs:///test.txt
Copying from ...
/ [1 files][ 0.0 B/ 0.0 B]
Operation completed over 1 objects.
```

If the total size cannot be calculated, the uploaded size should still be displayed like:
`/ [1 files][ 5.0 B/ - ]`

Reproduce the issue with `echo test | gsutil cp - gs:///test.txt`, then trace the `cp` path for stdin uploads and progress reporting. Done means the progress output reports the uploaded byte count while leaving the total size unknown, as in the example.

Written by the indexing model from the issue text.