[wasm] Also test structured stack trace

test/mjsunit/mjsunit.js

Index: test/mjsunit/mjsunit.js
diff --git a/test/mjsunit/mjsunit.js b/test/mjsunit/mjsunit.js
index 9b07953c8aa22a24cd1386e1f212027dab0c7e2f..6a7c2da9e47d1ca56b52c98b3afbd2a2b6d72b6c 100644
--- a/test/mjsunit/mjsunit.js
+++ b/test/mjsunit/mjsunit.js
@@ -114,6 +114,9 @@ var assertUnreachable;
 var assertOptimized;
 var assertUnoptimized;
 
+// Assert that a string contains another expected substring.
+var assertContains;
+
 
 (function () {  // Scope for utility functions.
 
@@ -416,6 +419,12 @@ var assertUnoptimized;
     throw new MjsUnitAssertionError(message);
   };
 
+  assertContains = function(sub, value, name_opt) {
+    if (value == null ? (sub != null) : value.indexOf(sub) == -1) {
+      fail("contains '" + String(sub) + "'", value, name_opt);
+    }
+  };
+
   var OptimizationStatusImpl = undefined;
 
   var OptimizationStatus = function(fun, sync_opt) {