Add a support for a slow marker in status files.

Add a support for a slow marker in status files.

The reasoning for this is that we want to have a sufficiently low
timeout to catch performance regressions, but still want to maintain
the support for having a few tests that takes a longer time to
complete.

This cl adds 2 slow functions, I will add more if any additional tests timeout on the buildbot.
Committed: https://code.google.com/p/dart/source/detail?r=10714

[ahe, 2012-08-15 11:34:13]

LGTM, but please have Bill take a look before submitting.

[Bill Hesse, 2012-08-15 11:41:03]

LGTM.

https://chromiumcodereview.appspot.com/10854156/diff/1/tools/testing/dart/tes...
File tools/testing/dart/test_runner.dart (right):

https://chromiumcodereview.appspot.com/10854156/diff/1/tools/testing/dart/tes...
tools/testing/dart/test_runner.dart:135: 
How about 
  if (expectedOutcomes.contains(SLOW)) {
    return SLOW_TIMEOUT_MULTIPLIER * configuration['timeout'];
} else {
  return configuration['timeout'];
}
or even 
 => expectedOutcomes.contains(SLOW) ?
   ... :
   ... ;