[wasm] enable wasm structured cloning in specific cases

third_party/WebKit/LayoutTests/http/tests/wasm/resources/service-worker.js

+var port;
+
+importScripts('load_wasm.js');
+
+self.onmessage = function(e) {
+    var message = e.data;
+    if ('port' in message) {
+        port = message.port;
+    }
+};
+
+// And an event listener:
+self.addEventListener('message', function(e) {
+    var message = e.data;
+    if ("compile" in message) {
+        createWasmModule()
+            .then(m => {
+                try {
+                    port.postMessage({type:"OK", module:m});
+                } catch (e) {
+                    port.postMessage({type:"SEND ERROR"});
+                }
+            })
+            .catch(e => port.postMessage({type:"OTHER ERROR"}));
+    }
+});