[BUGFIX beta] Avoid allocating a binding map in meta when possible

[mmun]

Before this PR, the connectBindings phase of Ember.Object creation would call meta.clearBindings() on every single object. This causes an extra EmptyObject to be allocated for every Ember.Object. The worst part is that it is never used on instances.

This change works around the issue making clearBindings simply setting _bindings to undefined in meta. We could likely remove this field completely if we had separate Meta classes for instances and classes.

[stefanpenner]

Good catch, bugfix beta ? Or should this ride the canary train.

[mmun]

Should be completely safe to do that. Even if we did use the binding map on instances, calling metal.writeBindings(...) would create the map if it were undefined. There's no point in eagerly instantiating on clear.

[stefanpenner]

There's no point in eagerly instantiating on clear.

👍

[stefanpenner]

@mmun I have noticed many related issues to this over time, thanks for also adding a test. I MUCH suspect more low hanging fruit like this is present.