[webkit-dev] Existing metrics for deprecated features

[Adam Barth]

In connection with the thread on webkitPostMessage, I took a look at
what sorts of metrics we have currently for depreciated features.  We
have high quality data for two groups of APIs:

For mutation events, we measure what percent of Documents have
listeners for various kinds of mutation events:

DOMAPI.PerDocumentMutationEventUsage.DOMCharacterDataModified: 2.85%
of all Documents
DOMAPI.PerDocumentMutationEventUsage.DOMNodeInserted: 4.78% of all Documents
DOMAPI.PerDocumentMutationEventUsage.DOMNodeInsertedIntoDocument:
0.21% of all Documents
DOMAPI.PerDocumentMutationEventUsage.DOMNodeRemoved: 0.07% of all Documents
DOMAPI.PerDocumentMutationEventUsage.DOMNodeRemovedFromDocument:
0.0003% of all Documents
DOMAPI.PerDocumentMutationEventUsage.DOMSubtreeModified: 2.30% of all Documents