Fixes: https://github.com/w3c/html/issues/785

[blurbusters]

Fix for #785 relating to clarifying callback rate for requestAnimationFrame(). Thoughtful wording changes agreed by multiple independent industry representatives. For detailed info, see 2017-04-21 comment to githib #785

Also strengthens future path towards: #375

[chaals]

@mdrejhon thanks for this. Just to be clear, the substantive change that affects conformance is a new requirement that user agents don't arbitrarily restrict refresh rates, which according to your statements in #785 is already the case for blink and webkit - meaning we have sufficient interoperability for putting something into a Recommendation, and seems to be the direction in which both Firefox and Edge are moving.

If I got that wrong, please clarify in #785 …

[blurbusters]

Yes.

(just one minor clarification -- you got one engine in the wrong category)

In very brief summarization, #785 says:

-- PASS: Blink/Gecko/Webkit aka Chrome/Opera/FireFox/Safari are the ones that are currently compliant. (All tested at 144fps at 144Hz, plus Chrome/FireFox tested up to 240fps at 240Hz.)

-- FAIL: Trident/EdgeHTML aka IE/Edge has the arbitrary hardcoded cap (probably 1-line code) that becomes hit in unconstrained situations such as high-performance desktops. As soon as your display exceed exactly 105Hz, the framerate of requestAnimationFrame() suddenly halves (even at <1% CPU), all versions of Windows 7 and up.