[mathml-tests] Import MathML tests for the id and class attributes. (#3987)

This commit imports tests from the MathML in HTML5 test suite to check the use
of id and class attributes on MathML elements:

- Javascript (getElementById and getElementsByClassName)
- CSS selectors (#id and .class)
- id used as a fragment identifier in URIs

@jgraham Yet another series of tests. Reviewed and integrated into WebKit testsuite (https://trac.webkit.org/browser/trunk/LayoutTests/imported/mathml-in-html5/mathml/relations/html5-tree). They currently pass on Gecko and WebKit.

View on GitHub: https://github.com/w3c/web-platform-tests/pull/3987

Received on Monday, 17 October 2016 11:57:17 UTC