Introduce a PrototypeIterator template and use it all over the place

src/json-stringifier.h

Index: src/json-stringifier.h
diff --git a/src/json-stringifier.h b/src/json-stringifier.h
index 0b5abbcdc9e1c0303f890e3cb4d33de08ee114a7..b8720d1e88bd137abd26a57251375931de31fd4a 100644
--- a/src/json-stringifier.h
+++ b/src/json-stringifier.h
@@ -8,6 +8,7 @@
 #include "src/v8.h"
 
 #include "src/conversions.h"
+#include "src/prototype-iterator.h"
 #include "src/utils.h"
 
 namespace v8 {
@@ -630,8 +631,8 @@ BasicJsonStringifier::Result BasicJsonStringifier::SerializeJSObject(
   Result stack_push = StackPush(object);
   if (stack_push != SUCCESS) return stack_push;
   if (object->IsJSGlobalProxy()) {
-    object = Handle<JSObject>(
-                 JSObject::cast(object->GetPrototype()), isolate_);
+    object = Handle<JSObject>(JSObject::cast(SAFE_GET_PROTOTYPE_FAST(*object)),
+                              isolate_);
     ASSERT(object->IsGlobalObject());
   }