Enable V8BasedStructuredClone by default.

third_party/WebKit/LayoutTests/fast/dom/Window/script-tests/postmessage-test.js

 if (window.testRunner) {
     testRunner.dumpAsText();
     testRunner.waitUntilDone();
 }
 
 var console = document.getElementById("console");
 
 var messages = [];
 var evalThunks = [];
 
@@ skipping 157 matching lines @@
         var value = eval(message);
         postMessage(value, "*", transferables);
         if (shouldThrow)
             console.innerHTML += "FAIL: 'postMessage("+message+")' should throw but didn't<br>";
         messages.push(expected || message);
         if (expected == "evalThunk") {
             evalThunks.push(evalThunk);
         }
     } catch(e) {
         if (shouldThrow) {
-            if (expectedException === undefined || expectedException == e.code || expectedException == e) {
+            if (expectedException === undefined || expectedException == e.code || expectedException == e || e instanceof expectedException) {
                 console.innerHTML += "PASS: 'postMessage("+message+")' threw " + escapeHTML(e) + "<br>";
             } else {
                 console.innerHTML += "FAIL: 'postMessage("+message+")' threw " + escapeHTML(e) + ", was expecting " + escapeHTML(expectedException) + "<br>";
             }
         } else
             console.innerHTML += "FAIL: 'postMessage("+message+")' should not throw but threw " + e + "<br>";
     }
 }