[test_runner] Use 'line' progress indicator by default when stdout is not a terminal

When the test runner output is piped to a file, 'compact' progress
indicator prints carriage returns to the file.

To avoid adding carriage returns to text files, only use 'compact'
indicator when stdout is a terminal. Otherwise use 'line' indicator.

Change-Id: Ic8ca111059799876caf401d3b040a5d3b5a7c731
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/431861
Reviewed-by: Bob Nystrom <[email protected]>
Commit-Queue: Ömer Ağacan <[email protected]>

Author: osa1

pkg/test_runner/lib/src/options.dart

@@ -180,7 +180,9 @@ test options, specifying how tests should be run.''')
     ..addOption('progress',
         abbr: 'p',
         allowed: Progress.names,
-        defaultsTo: Progress.compact.name,
+        defaultsTo: stdioType(stdout) == StdioType.terminal
+            ? Progress.compact.name
+            : Progress.line.name,
         help: '''Progress indication mode.
 
 Allowed values are:

pkg/test_runner/test/options_test.dart

@@ -18,7 +18,6 @@ void main() {
 void testDefaults() {
   // TODO(rnystrom): Test other options.
   var configuration = parseConfiguration([]);
-  Expect.equals(Progress.compact, configuration.progress);
   Expect.equals(NnbdMode.strong, configuration.nnbdMode);
 }