Add support for native ports in the vm.

runtime/vm/dart_api_impl.h

Index: runtime/vm/dart_api_impl.h
===================================================================
--- runtime/vm/dart_api_impl.h	(revision 3743)
+++ runtime/vm/dart_api_impl.h	(working copy)
@@ -123,6 +123,20 @@
   static uword Reallocate(uword ptr, intptr_t old_size, intptr_t new_size);
 };
 
+class IsolateSaver {
+ public:
+  explicit IsolateSaver(Isolate* current_isolate)
+      : saved_isolate_(current_isolate) {
+  }
+  ~IsolateSaver() {
+    Isolate::SetCurrent(saved_isolate_);
+  }
+ private:
+  Isolate* saved_isolate_;
+
+  DISALLOW_COPY_AND_ASSIGN(IsolateSaver);
+};
+
 }  // namespace dart.
 
 #endif  // VM_DART_API_IMPL_H_