Implement read methods on FileReaderSync

Upstreamed from servo/servo#19511 [ci skip]

FileAPI/FileReaderSync.worker.js

@@ -1,28 +1,56 @@
 importScripts("/resources/testharness.js");
 
-var blob, readerSync;
-setup(function() {
-  readerSync = new FileReaderSync();
-  blob = new Blob(["test"]);
+var blob, empty_blob, readerSync;
+setup(() => {
+    readerSync = new FileReaderSync();
+    blob = new Blob(["test"]);
+    empty_blob = new Blob();
 });
 
-test(function() {
-  assert_true(readerSync instanceof FileReaderSync);
+test(() => {
+    assert_true(readerSync instanceof FileReaderSync);
 }, "Interface");
 
-test(function() {
-  var text = readerSync.readAsText(blob);
-  assert_equals(text, "test");
+test(() => {
+    var text = readerSync.readAsText(blob);
+    assert_equals(text, "test");
 }, "readAsText");
 
-test(function() {
-  var data = readerSync.readAsDataURL(blob);
-  assert_equals(data.indexOf("data:"), 0);
+test(() => {
+    var text = readerSync.readAsText(empty_blob);
+    assert_equals(text, "");
+}, "readAsText with empty blob");
+
+test(() => {
+    var data = readerSync.readAsDataURL(blob);
+    assert_equals(data.indexOf("data:"), 0);
 }, "readAsDataURL");
 
-test(function() {
-  var data = readerSync.readAsArrayBuffer(blob);
-  assert_true(data instanceof ArrayBuffer);
+test(() => {
+    var data = readerSync.readAsDataURL(empty_blob);
+    assert_equals(data.indexOf("data:"), 0);
+}, "readAsDataURL with empty blob");
+
+test(() => {
+    var data = readerSync.readAsBinaryString(blob);
+    assert_equals(data, "test");
+}, "readAsBinaryString");
+
+test(() => {
+    var data = readerSync.readAsBinaryString(empty_blob);
+    assert_equals(data, "");
+}, "readAsBinaryString with empty blob");
+
+test(() => {
+    var data = readerSync.readAsArrayBuffer(blob);
+    assert_true(data instanceof ArrayBuffer);
+    assert_equals(data.byteLength, "test".length);
 }, "readAsArrayBuffer");
 
+test(() => {
+    var data = readerSync.readAsArrayBuffer(empty_blob);
+    assert_true(data instanceof ArrayBuffer);
+    assert_equals(data.byteLength, 0);
+}, "readAsArrayBuffer with empty blob");
+
 done();