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

runtime/bin/vmstats_impl_macos.cc

Index: runtime/bin/vmstats_impl_macos.cc
===================================================================
--- runtime/bin/vmstats_impl_macos.cc	(revision 0)
+++ runtime/bin/vmstats_impl_macos.cc	(revision 0)
@@ -0,0 +1,32 @@
+// 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_MACOS)
+
+#include "bin/vmstats_impl.h"
+
+#include <signal.h>  // NOLINT
+
+
+static void sig_handler(int sig, siginfo_t* siginfo, void*) {
+  if (sig == SIGQUIT) {
+    VmStats::DumpStack();
+  } else {
+    FATAL1("unrequested signal %d received\n", sig);
+  }
+}
+
+void VmStats::Initialize() {
+  // Enable SIGQUIT (ctrl-\) stack dumps.
+  struct sigaction sigact;
+  memset(&sigact, '\0', sizeof(sigact));
+  sigact.sa_sigaction = sig_handler;
+  sigact.sa_flags = SA_SIGINFO;
+  if (sigaction(SIGQUIT, &sigact, NULL) < 0) {
+    perror("sigaction");
+  }
+}
+
+#endif  // defined(TARGET_OS_MACOS)