The latest spec expects Canvas2d to have function getTransform() (https://html.spec.whatwg.org/multipage/scripting.html#dom-context-2d-gettransform) which returns a newly created DOMMatrix representing a copy of the current transformation matrix matrix of the context.

In particular, the spec notes that "This returned object is not live, so updating it will not affect the current transformation matrix, and updating the current transformation matrix will not affect an already returned DOMMatrix.".
(My doubt is whether the returned entity should be DOMMatrixReadOnly instead of DOMMatrix).

Note that at the time of writing, the function is actually implemented as "attribute SVGMatrix currentTransform;".

I am assigning this to myself because this is similar to another bug I have ( crbug.com/289572 ) but it'll take sometime for me to start. Anyone who want to implement this right now can ask it from me.