[MERGE #2198 @rajatd] Keep property records live on IteratorObjectEnumerator

Merge pull request #2198 from rajatd:iteratorEnum

We need to keep property records for properties being enumerated live during enumeration. For dynamic objects, type handlers hold references to property records and for non-existent properties, we have code in ForInObjectEnumerator::MoveAndGetNext to keep the new records live.

Taking care of this case for Proxies which use IteratorObjectEnumerator

Author: rajatd

lib/Runtime/Library/IteratorObjectEnumerator.cpp

@@ -45,6 +45,11 @@ namespace Js
             {
                 JavascriptString* propertyName = JavascriptConversion::ToString(currentIndex, scriptContext);
                 GetScriptContext()->GetOrAddPropertyRecord(propertyName->GetString(), propertyName->GetLength(), &propertyRecord);
+
+                // Need to keep property records alive during enumeration to prevent collection
+                // and eventual reuse during the same enumeration. For DynamicObjects, property
+                // records are kept alive by type handlers.
+                this->propertyRecords.Prepend(iteratorObject->GetRecycler(), propertyRecord);
             }
 
             propertyId = propertyRecord->GetPropertyId();

lib/Runtime/Library/IteratorObjectEnumerator.h

@@ -21,6 +21,7 @@ namespace Js
         RecyclableObject* iteratorObject;
         Var value;
         BOOL done;
+        SListBase<Js::PropertyRecord const *> propertyRecords;
     };
 
 }