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..2a7b33fb64e6fd654f1b6d08c9a48727742067f4
--- /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();
+}