Cleanup app snapshots on isolate/vm exit.

runtime/bin/extensions.h

Index: runtime/bin/extensions.h
diff --git a/runtime/bin/extensions.h b/runtime/bin/extensions.h
index 3739c434f4e56180f4d99428722a34e1ca87f80a..d4c7b33001d453f5efeca1d2a284deebeefe1688 100644
--- a/runtime/bin/extensions.h
+++ b/runtime/bin/extensions.h
@@ -20,8 +20,9 @@ class Extensions {
                                    Dart_Handle parent_library);
 
   // Platform-specific implementations.
-  static void* LoadExtensionLibrary(const char* library_file);
+  static void* LoadLibrary(const char* library_file);
   static void* ResolveSymbol(void* lib_handle, const char* symbol);
+  static void UnloadLibrary(void* lib_handle);
 
  private:
   static Dart_Handle GetError();