[wasm] Also test structured stack trace

test/intl/assert.js

Index: test/intl/assert.js
diff --git a/test/intl/assert.js b/test/intl/assert.js
index e17615267ae327ea25b60db0a67e99d11fbb6a49..8af48fa44c6e4a35cca6a511f9b300249bdb1c3a 100644
--- a/test/intl/assert.js
+++ b/test/intl/assert.js
@@ -109,6 +109,16 @@ function assertEquals(expected, found, user_message = '') {
 
 
 /**
+ * Throws if value does not contain sub.
+ */
+function assertContains(value, sub, user_message = '') {
+  if (value == null ? (sub != null) : value.indexOf(sub) == -1) {
+    fail("contains '" + String(sub) + "'", value, user_message);
+  }
+}
+
+
+/**
  * Throws if value is false.
  */
 function assertTrue(value, user_message = '') {