Use downloadToFile option when XHR downloads a Blob

LayoutTests/http/tests/xmlhttprequest/resources/xmlhttprequest-response-type-blob.js

Index: LayoutTests/http/tests/xmlhttprequest/resources/xmlhttprequest-response-type-blob.js
diff --git a/LayoutTests/http/tests/xmlhttprequest/resources/xmlhttprequest-response-type-blob.js b/LayoutTests/http/tests/xmlhttprequest/resources/xmlhttprequest-response-type-blob.js
new file mode 100644
index 0000000000000000000000000000000000000000..9f1b5f6446ee5dcf42245f62c1c1b9ca4d5672bd
--- /dev/null
+++ b/LayoutTests/http/tests/xmlhttprequest/resources/xmlhttprequest-response-type-blob.js
@@ -0,0 +1,25 @@
+var global = window;
+
+try {
+    global.req = new XMLHttpRequest;
+    req.responseType = 'blob';
+    req.open('GET', 'resources/get.txt', true);
+    req.onreadystatechange = function() {
+        if (req.readyState == 4) {
+            shouldBe('req.status', '200');
+            shouldBe('req.response.size', '4');
+            var reader = new FileReader();
+            reader.onload = function (evt) {
+                global.buffer = evt.target.result;
+                shouldBeEqualToString('buffer', 'PASS');
+                testPassed('XHR with responseType="blob" succeeded');
+                finishJSTest();
+            };
+            reader.readAsText(req.response, 'utf-8');
+        }
+    };
+    req.send(null);
+} catch (e) {
+    testFailed('failed to create XMLHttpRequest with exception: ' + e.message);
+    finishJSTest();
+}