Dump stack trace on segfault in the VM.

runtime/bin/platform_macos.cc

Index: runtime/bin/platform_macos.cc
diff --git a/runtime/bin/platform_macos.cc b/runtime/bin/platform_macos.cc
index 35e910706ac3da97eeee42b54ecdc7173cd0fd32..01c7cbb65ced9bdebb699767629222393e358193 100644
--- a/runtime/bin/platform_macos.cc
+++ b/runtime/bin/platform_macos.cc
@@ -28,6 +28,12 @@ char* Platform::resolved_executable_name_ = NULL;
 int Platform::script_index_ = 1;
 char** Platform::argv_ = NULL;
 
+
+static void segv_handler(int signal, siginfo_t* siginfo, void* context) {
+  Dart_DumpNativeStackTrace(context);
+  abort();
+}
+
 bool Platform::Initialize() {
   // Turn off the signal handler for SIGPIPE as it causes the process
   // to terminate on writing to a closed pipe. Without the signal
@@ -39,6 +45,20 @@ bool Platform::Initialize() {
     perror("Setting signal handler failed");
     return false;
   }
+  act.sa_flags = SA_SIGINFO;
+  act.sa_sigaction = &segv_handler;
+  if (sigemptyset(&act.sa_mask) != 0) {
+    perror("sigemptyset() failed.");
+    return false;
+  }
+  if (sigaddset(&act.sa_mask, SIGPROF) != 0) {
+    perror("sigaddset() failed");
+    return false;
+  }
+  if (sigaction(SIGSEGV, &act, NULL) != 0) {
+    perror("sigaction() failed.");
+    return false;
+  }
   return true;
 }