Reload native extensions when starting from a snapshot.

runtime/bin/dartutils.h

Index: runtime/bin/dartutils.h
diff --git a/runtime/bin/dartutils.h b/runtime/bin/dartutils.h
index c2ab3fb36f4a2cc6ef22657b3a66fc919effe5cf..02478ba98e9a3d5a1a4c713b2916612aa3ac1908 100644
--- a/runtime/bin/dartutils.h
+++ b/runtime/bin/dartutils.h
@@ -125,6 +125,7 @@ class DartUtils {
   static bool IsDartBuiltinLibURL(const char* url_name);
   static bool IsHttpSchemeURL(const char* url_name);
   static const char* RemoveScheme(const char* url);
+  static char* DirName(const char* url);
   static void* MapExecutable(const char* name, intptr_t* file_len);
   static void* OpenFile(const char* name, bool write);
   static void ReadFile(const uint8_t** data, intptr_t* file_len, void* stream);