- Add assertions in MutexLocker/MonitorLocker to ensure that the code enclosed

runtime/vm/os_thread_linux.cc

Index: runtime/vm/os_thread_linux.cc
diff --git a/runtime/vm/os_thread_linux.cc b/runtime/vm/os_thread_linux.cc
index f82123306e0c9d8141b3810da7edf58869f618a3..a0e68f1870e5b3222039a3b5467aea05d29cd214 100644
--- a/runtime/vm/os_thread_linux.cc
+++ b/runtime/vm/os_thread_linux.cc
@@ -341,6 +341,22 @@ Monitor::~Monitor() {
 }
 
 
+bool Monitor::TryEnter() {
+  int result = pthread_mutex_trylock(data_.mutex());
+  // Return false if the lock is busy and locking failed.
+  if (result == EBUSY) {
+    return false;
+  }
+  ASSERT_PTHREAD_SUCCESS(result);  // Verify no other errors.
+#if defined(DEBUG)
+  // When running with assertions enabled we track the owner.
+  ASSERT(owner_ == OSThread::kInvalidThreadId);
+  owner_ = OSThread::GetCurrentThreadId();
+#endif  // defined(DEBUG)
+  return true;
+}
+
+
 void Monitor::Enter() {
   int result = pthread_mutex_lock(data_.mutex());
   VALIDATE_PTHREAD_RESULT(result);