Only collect 1 stack trace when a test timeouts on mac

tools/testing/dart/test_runner.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /**
  * Classes and methods for executing tests.
  *
  * This module includes:
  * - Managing parallel execution of tests, including timeout checks.
  * - Evaluating the output of each test as pass/fail/crash/timeout.
@@ skipping 1852 matching lines @@
                 })
                 .catchError(
                     (error) => print("Error when printing stack trace: $error"))
                 .whenComplete(() {
                   if (!process.kill()) {
                     DebugLogger.error("Unable to kill ${process.pid}");
                   }
                 });
               } else if (io.Platform.isMacOS) {
                 // Try to print stack traces of the timed out process.
+                // `sample` is a sampling profiler but we ask it sample for 1
+                // second with a 4 second delay between samples so that we only
+                // sample the threads once.
                 io.Process.run('/usr/bin/sample',
-                               ['${process.pid}', '1', '1', '-mayDie'])
+                               ['${process.pid}', '1', '4000', '-mayDie'])
                 .then((result) {
                   io.stdout.write(result.stdout);
                   io.stderr.write(result.stderr);
                 })
                 .catchError(
                     (error) => print("Error when printing stack trace: $error"))
                 .whenComplete(() {
                   if (!process.kill()) {
                     DebugLogger.error("Unable to kill ${process.pid}");
                   }
@@ skipping 1190 matching lines @@
     }
   }
 
   void eventAllTestsDone() {
     for (var listener in _eventListener) {
       listener.allDone();
     }
     _allDone();
   }
 }