Optionally create internal fields on global proxy objects

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index c10056f56b3ae6acc2273d19afe260e872095565..d1733df37486cbf596d9153a1b4f9aacb7c459fb 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -8509,6 +8509,8 @@ class JSGlobalProxy : public JSObject {
   static const int kNativeContextOffset = JSObject::kHeaderSize;
   static const int kHashOffset = kNativeContextOffset + kPointerSize;
   static const int kSize = kHashOffset + kPointerSize;
+  static const int kSizeWithInternalFields =
+      kSize + v8::Context::kProxyInternalFieldCount * kPointerSize;
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(JSGlobalProxy);