[XMLHttpRequest] Stop throwing for network error in async mode

LayoutTests/fast/files/resources/apply-blob-url-to-xhr.js

+function log(message)
+{
+    if (self.importScripts) {
+        postMessage(message);
+    } else {
+        document.getElementById('console').appendChild(document.createTextNode(message + "\n"));
+    }
+}
+
+var uuidRegex = new RegExp('[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}');
+
+function replaceUUID(s)
+{
+    return s.replace(uuidRegex, 'UUID');
+}
+
+function sendXMLHttpRequestSync(method, url)
+{
+    var xhr = new XMLHttpRequest();
+    xhr.open(method, url, false);
+    try {
+        xhr.send();
+        log("Status: " + xhr.status);
+        log("Response: " + xhr.responseText);
+    } catch (error) {
+        log("Received exception, code: " + error.code + ", name: " + error.name + ", message: " + replaceUUID(error.message));
+    }
+}
+
+function sendXMLHttpRequestAsync(method, url)
+{
+    return new Promise(function (resolve) {
+        var xhr = new XMLHttpRequest();
+
+        xhr.onload = function()
+        {
+            log("Status: " + xhr.status);
+            log("Response: " + xhr.responseText);
+        };
+        xhr.onerror = function()
+        {
+            log("Error event is dispatched");
+        };
+        xhr.onloadend = function()
+        {
+            resolve();
+        };
+
+        xhr.open(method, url, true);
+        try {
+            xhr.send();
+        } catch (error) {
+            log("Received exception, code: " + error.code + ", name: " + error.name + ", message: " + replaceUUID(error.message));
+        }
+    });
+}
+
+function runXHRs(file)
+{
+    var fileURL = URL.createObjectURL(file);
+
+    log("Test that sync XMLHttpRequest GET succeeds.");
+    sendXMLHttpRequestSync("GET", fileURL);
+
+    log("Test that sync XMLHttpRequest POST fails.");
+    sendXMLHttpRequestSync("POST", fileURL);
+
+    log("Test that sync XMLHttpRequest GET fails after the blob URL is revoked.");
+    URL.revokeObjectURL(fileURL);
+    sendXMLHttpRequestSync("GET", fileURL);
+
+    fileURL = URL.createObjectURL(file);
+
+    log("Test that async XMLHttpRequest GET succeeds.");
+    sendXMLHttpRequestAsync("GET", fileURL).then(function()
+    {
+        log("Test that async XMLHttpRequest POST fails.");
+        return sendXMLHttpRequestAsync("POST", fileURL);
+    }).then(function()
+    {
+        log("Test that async XMLHttpRequest GET fails after the blob URL is revoked.");
+        URL.revokeObjectURL(fileURL);
+        return sendXMLHttpRequestAsync("GET", fileURL);
+    }).then(function()
+    {
+        log("DONE");
+        if (!self.importScripts && testRunner.notifyDone)
+            testRunner.notifyDone();
+    });
+}
+
+if (self.importScripts) {
+    onmessage = function(event)
+    {
+        runXHRs(event.data);
+    };
+}