Have DataTransferItemList.add() methods return the added item

LayoutTests/fast/events/drag-dataTransferItemList-file-handling-expected.txt

Index: LayoutTests/fast/events/drag-dataTransferItemList-file-handling-expected.txt
diff --git a/LayoutTests/fast/events/drag-dataTransferItemList-file-handling-expected.txt b/LayoutTests/fast/events/drag-dataTransferItemList-file-handling-expected.txt
index 0720a97219b0763c0e30185367f717f58fe0b651..649d322e9cae115310d4fb7e24b2228550cd325a 100644
--- a/LayoutTests/fast/events/drag-dataTransferItemList-file-handling-expected.txt
+++ b/LayoutTests/fast/events/drag-dataTransferItemList-file-handling-expected.txt
@@ -1,8 +1,20 @@
-To manually test, select a text file for the file input element, and then drag 'Drag Me' to 'Drop Here' and drop. Several lines that say 'PASS' should appear below. 
+To manually test, select a text file for the file input element, and then drag 'Drag Me' to 'Drop Here' and drop. 
 
 Drag Me
 Drop Here
-PASS: 1 === 1
-PASS: file === file
-PASS: text/plain === text/plain
+Tests DataTransferItemList file handling
+
+On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
+
+
+PASS testItem.kind is "file"
+PASS testItem.type is "text/plain"
+PASS testItems.length is 1
+PASS testItems.add(testFile) is null
+PASS testItems.length is 1
+PASS testItems[0].kind is "file"
+PASS testItems[0].type is "text/plain"
+PASS successfullyParsed is true
+
+TEST COMPLETE