Add a use counter for Attr.prototype.cloneNode()
This is being measured as requested in a spec discussion:
https://github.com/whatwg/dom/issues/102#issuecomment-158833267
To avoid making a observable change to Attr.prototype, measure this
internally. This risks including internal uses, but there appear to be
none. All calls were checked and they seem to be for either parent or
child nodes of some kind, and Attr cannot be a parent or child.
Also, a deprecation message was added to see if it would be triggered
unexpectedly on any tests, but it was only emitted for tests that
actually clone attributes, as expected.
Drive-by: Drop an unused ShadowRoot::cloneNode() that was missed in
https://codereview.chromium.org/1482433003
BUG=305105
Review URL: https://codereview.chromium.org/1474083002
Cr-Commit-Position: refs/heads/master@{#361932}
4 files changed
