Flush stdout when printing perf values for ChromeOS in pyauto perf tests.

Flush stdout when printing perf values for ChromeOS in pyauto perf tests.

The pyauto-based perf tests output perf results in a special format, which
are extracted from stdout and stored for graphing purposes.  I encountered
a case where one of these specially-formatted perf output lines was broken
up by other, interleaved output, causing the perf value to be missed when
the output was parsed to search for perf values.  I believe that flushing
stdout immediately after printing each perf output line should fix this
problem.

BUG=None
TEST=None

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=112744

[Nirnimesh, 2011-12-02 18:00:07]

LGTM