Add the concept of a V8 extras exports object

test/mjsunit/debug-script.js

Index: test/mjsunit/debug-script.js
diff --git a/test/mjsunit/debug-script.js b/test/mjsunit/debug-script.js
index af1eb454d65d65061d01999ca60286366bae6a89..12a1f16d35fc697a1a40907a7b872bf0190b3c86 100644
--- a/test/mjsunit/debug-script.js
+++ b/test/mjsunit/debug-script.js
@@ -66,7 +66,7 @@ for (i = 0; i < scripts.length; i++) {
 }
 
 // This has to be updated if the number of native scripts change.
-assertEquals(%NativeScriptsCount(), named_native_count);
+assertEquals(%NativeScriptsCount() + %NativeExtrasCount(), named_native_count);
 // Only the 'gc' extension is loaded.
 assertEquals(1, extension_count);
 // This script and mjsunit.js has been loaded.  If using d8, d8 loads