VM: Fix deadlock in time line recording.

runtime/vm/os_thread_macos.cc

Index: runtime/vm/os_thread_macos.cc
diff --git a/runtime/vm/os_thread_macos.cc b/runtime/vm/os_thread_macos.cc
index 2fa58d85456e73334b5501e2b501079ca4070e90..478c1e090656fd439d153c5ae1d3874187bc73ff 100644
--- a/runtime/vm/os_thread_macos.cc
+++ b/runtime/vm/os_thread_macos.cc
@@ -217,7 +217,7 @@ void OSThread::GetThreadCpuUsage(ThreadId thread_id, int64_t* cpu_usage) {
 }
 
 
-Mutex::Mutex() {
+Mutex::Mutex(bool recursive) {
   pthread_mutexattr_t attr;
   int result = pthread_mutexattr_init(&attr);
   VALIDATE_PTHREAD_RESULT(result);
@@ -227,6 +227,11 @@ Mutex::Mutex() {
   VALIDATE_PTHREAD_RESULT(result);
 #endif  // defined(DEBUG)
 
+  if (recursive) {
+    result = pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE);
+    VALIDATE_PTHREAD_RESULT(result);
+  }
+
   result = pthread_mutex_init(data_.mutex(), &attr);
   // Verify that creating a pthread_mutex succeeded.
   VALIDATE_PTHREAD_RESULT(result);