Don't call getBoundingClientRect() directly

[annevk]

It's a public API, not a private API.

@domenic raised this in #55, but it doesn't appear to be fixed.

[domfarolino]

From #155:

For getBoudningClientRect lets used Domenic's text and file a bug against cssom-view asking for a name for this algorithm so we can refer to it directly.

Has this been done? Any progress here?

[szager-chromium]

Marking this as "duplicate", all further discussion should happen on issue #55.