Make loader lock new-allocated to avoid shutdown crash.

runtime/bin/loader.h

Index: runtime/bin/loader.h
diff --git a/runtime/bin/loader.h b/runtime/bin/loader.h
index 088ce2ecc39fa16f3daeddc6374749f6c7679ccb..1c8f4ad99497bfc9feb152a02ba58e9f72d0c050 100644
--- a/runtime/bin/loader.h
+++ b/runtime/bin/loader.h
@@ -37,6 +37,8 @@ class Loader {
     return error_;
   }
 
+  static void InitOnce();
+
  private:
   // The port assigned to our native message handler.
   Dart_Port port_;
@@ -120,7 +122,7 @@ class Loader {
   };
 
   // The map of active loaders.
-  static Mutex loader_infos_lock_;
+  static Mutex* loader_infos_lock_;
   static LoaderInfo* loader_infos_;
   static intptr_t loader_infos_length_;
   static intptr_t loader_infos_capacity_;