Added ctrl-\ command that dumps isolate stacks to dart binary.

runtime/bin/vmstats_impl_linux.cc

+// Copyright (c) 2013, 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.
+
+#include "platform/globals.h"
+#if defined(TARGET_OS_LINUX)
+
+#include "bin/vmstats_impl.h"
+
+#include <signal.h>  // NOLINT
+
+
+static void sig_handler(int sig) {
+  if (sig == SIGQUIT) {
+    VmStats::DumpStack();
+  }

[siva, 2013/04/04 00:47:15]

You should not be handling any other signals right so it should be an
UNREACHABLE or Fatal...

[Tom Ball, 2013/04/04 20:05:53]

Done.

+}
+
+void VmStats::Initialize() {
+  // Enable SIGQUIT (ctrl-\) stack dumps.
+  if (signal(SIGQUIT, sig_handler) == SIG_ERR) {

[siva, 2013/04/04 00:47:15]

You should be using the sigaction call here and not signal.
(from man page: The behavior of signal() varies across
UNIX versions, and has also varied historically across
different versions of Linux.   Avoid  its  use:
use sigaction(2) instead.).

sigaction always you to control the behavior of signal
delivery when you are inside a signal handler (that is
nested invocation of the signal handler).

[Tom Ball, 2013/04/04 20:05:53]

Replaced with sigaction, except for Windows because it only has signal
(http://www.suacommunity.com/dictionary/sigaction-entry.php).

+    perror("Adding SIGQUIT signal handler failed");
+  }
+}
+
+#endif  // defined(TARGET_OS_LINUX)