test.dart progress bar: a small tweak when --report is not used.

test.dart progress bar: a small tweak when --report is not used.

Committed: https://code.google.com/p/dart/source/detail?r=4190

[Siggi Cherem (dart-lang), 2012-02-10 22:48:18]

On my desktop if I run test.dart without --report I see the initial progress
bar, it goes away, and a couple secs later, the bar comes back (once the first
test is done running).

What I wanted to do was to only delete the old bar when we are printing a
report, but otherwise we keep it around. Let me know you'd like me to fix it
some other way (e.g. maybe put the clear as part of the first line of the
report?)

[Bill Hesse, 2012-02-13 09:23:22]

LGTM.