Implement DOMMatrix.fromMatrix

Also fixes `.multiply()` to use DOMMatrixInit.

Differential Revision: https://phabricator.services.mozilla.com/D35526

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1560462
gecko-commit: 237163b50c8cd1d309592b3a8c30db6ff7452e3d
gecko-integration-branch: central
gecko-reviewers: bzbarsky
diff --git a/css/geometry/support/dommatrix-test-util.js b/css/geometry/support/dommatrix-test-util.js
index c7299bc..af860e2 100644
--- a/css/geometry/support/dommatrix-test-util.js
+++ b/css/geometry/support/dommatrix-test-util.js
@@ -37,7 +37,7 @@
 
 function checkMatrix(actual, expected, { epsilon = 0 } = {}) {
   for (let member in expected) {
-    if (typeof expected[member] === "number") {
+    if (epsilon && typeof expected[member] === "number") {
       assert_approx_equals(actual[member], expected[member], epsilon, member);
     } else {
       assert_equals(actual[member], expected[member], member);