test.dart: Print stack traces of all threads when a test times out

tools/testing/dart/test_runner.dart

Index: tools/testing/dart/test_runner.dart
diff --git a/tools/testing/dart/test_runner.dart b/tools/testing/dart/test_runner.dart
index 132d0c6d7f3d6ffc5d84b467a290b11ff8dcbc9d..0f55b0ad154ec116357302bfb856e28bf1958a22 100644
--- a/tools/testing/dart/test_runner.dart
+++ b/tools/testing/dart/test_runner.dart
@@ -1854,9 +1854,19 @@ class RunningProcess {
           void timeoutHandler() {
             timedOut = true;
             if (process != null) {
-              if (!process.kill()) {
-                DebugLogger.error("Unable to kill ${process.pid}");
-              }
+              io.Process.run('gdb',

[rmacnak, 2016/09/07 19:33:47]

Only attempt to use gdb on Linux.

[Florian Schneider, 2016/09/07 21:02:58]

Done.

+                  ['--pid=${process.pid}',
+                   '--eval-command=thread apply all bt',
+                   '--eval-command=quit'])
+              .then((result) {
+                io.stdout.write(result.stdout);
+                io.stderr.write(result.stderr);
+              })

[siva, 2016/09/07 19:55:20]

Do we also need a catchError handler here to print a diagnostic message if gdb
fails to start.

We also have to be sure that the bots have the process attach capability set
(see /etc/sysctl.d/10-ptrace.conf).

[Florian Schneider, 2016/09/07 21:02:58]

Yes. Added printing. Also, I should only invoke gdb if it is available on the
system. Is there a standard way in Dart to find if gdb is installed on a system?

[Bill Hesse, 2016/09/08 14:58:01]

I would just run "which gdb" in a subprocess, and check the return code.

+              .whenComplete(() {
+                if (!process.kill()) {
+                  DebugLogger.error("Unable to kill ${process.pid}");
+                }
+              });
             }
           }