Bug 1571567 - Fix no-fallthrough errors in /layout. r=dholbert

Differential Revision: https://phabricator.services.mozilla.com/D40876

--HG--
extra : moz-landing-system : lando

layout/style/test/animation_utils.js

@@ -516,6 +516,7 @@ const ExpectComparisonTo = {
           };
           break;
         }
+      // fall through
       case "transform":
         normalize = convertTo3dMatrix;
         compare = matricesRoughlyEqual;