[GeometryInterface] add transformPoint(point) function.

third_party/WebKit/LayoutTests/fast/dom/resources/geometry-interfaces-test-helpers.js

 function assert_identity_2d_matrix(actual) {
   assert_true(actual instanceof DOMMatrixReadOnly);
   assert_true(actual.is2D, "is2D");
   assert_true(actual.isIdentity, "isIdentity");
   assert_identity_matrix(actual);
 }
 
 function assert_identity_3d_matrix(actual) {
   assert_true(actual instanceof DOMMatrixReadOnly);
   assert_false(actual.is2D, "is2D");
@@ skipping 45 matching lines @@
 
 function assert_array_almost_equals(actual, expected) {
   for (var i = 0; i < actual.length; i++) {
     assert_equals(actual[i].toFixed(10), expected[i].toFixed(10));
   }
 }
 
 function assert_matrix_almost_equals(actual, expected) {
   assert_array_almost_equals(actual.toFloat64Array(), expected.toFloat64Array());
 }
+
+function assert_point_equals(actual, expected) {
+  assert_equals(actual.x, expected.x, "point equality: x differs");
+  assert_equals(actual.y, expected.y, "point equality: y differs");
+  assert_equals(actual.z, expected.z, "point equality: z differs");
+  assert_equals(actual.w, expected.w, "point equality: w differs");
+}