Fix for issue 23908 - error message reports the exact error when a native extension fails to load.

runtime/bin/extensions.h

Index: runtime/bin/extensions.h
diff --git a/runtime/bin/extensions.h b/runtime/bin/extensions.h
index 25dbfeb13092fb047042a1ea2178af9ba5dd3f28..7911131cded6e11ede85e1fe243b6419114f2157 100644
--- a/runtime/bin/extensions.h
+++ b/runtime/bin/extensions.h
@@ -22,8 +22,11 @@ class Extensions {
                                    Dart_Handle parent_library);
 
   // Platform-specific implementations.
-  static void* LoadExtensionLibrary(const char* library_file);
-  static void* ResolveSymbol(void* lib_handle, const char* symbol);
+  static Dart_Handle LoadExtensionLibrary(const char* library_file,
+                                          void** library);
+  static Dart_Handle ResolveSymbol(void* lib_handle,
+                                   const char* symbol,
+                                   void** init_func);
 
  private:
   // The returned string must be freed.