Re-enable freezing of Object.observe changeRecords now that freezing is faster.

src/object-observe.js

Index: src/object-observe.js
diff --git a/src/object-observe.js b/src/object-observe.js
index b28f928a4849a7da49e4350dd493645c53b6c3cc..5ca70bcff565c8daf8fc15d8343aee3bbd0b59c8 100644
--- a/src/object-observe.js
+++ b/src/object-observe.js
@@ -308,10 +308,8 @@ function EnqueueSpliceRecord(array, index, removed, deleteCount, addedCount) {
   };
 
   changeRecord.removed.length = deleteCount;
-  // TODO(rafaelw): This breaks spec-compliance. Re-enable when freezing isn't
-  // slow.
-  // ObjectFreeze(changeRecord);
-  // ObjectFreeze(changeRecord.removed);
+  ObjectFreeze(changeRecord);
+  ObjectFreeze(changeRecord.removed);

[adamk, 2013/05/23 21:12:39]

I'd leave this out for now, as it basically doubles the cost of creating a
splice record (create the removed array, then create a dictionary backing store
and copy everything over).

[rafaelw, 2013/05/23 22:53:18]

I went back and tried as hard as I could to create a case where freezing the
removed array impacted the over-all time noticeably -- and failed to produce
anything that was obviously not in the noise.

I think it's fine to leave this in.

On 2013/05/23 21:12:39, adamk wrote:

[adamk, 2013/05/23 22:55:49]

Sounds good to me, thanks for doing the footwork to verify this.

   EnqueueChangeRecord(changeRecord, objectInfo.changeObservers);
 }
 
@@ -323,9 +321,7 @@ function NotifyChange(type, object, name, oldValue) {
   var changeRecord = (arguments.length < 4) ?
       { type: type, object: object, name: name } :
       { type: type, object: object, name: name, oldValue: oldValue };
-  // TODO(rafaelw): This breaks spec-compliance. Re-enable when freezing isn't
-  // slow.
-  // ObjectFreeze(changeRecord);
+  ObjectFreeze(changeRecord);
   EnqueueChangeRecord(changeRecord, objectInfo.changeObservers);
 }
 
@@ -351,9 +347,7 @@ function ObjectNotifierNotify(changeRecord) {
     %DefineOrRedefineDataProperty(newRecord, prop, changeRecord[prop],
         READ_ONLY + DONT_DELETE);
   }
-  // TODO(rafaelw): This breaks spec-compliance. Re-enable when freezing isn't
-  // slow.
-  // ObjectFreeze(newRecord);
+  ObjectFreeze(newRecord);
 
   EnqueueChangeRecord(newRecord, objectInfo.changeObservers);
 }