FileReader needs addEventListener
https://bugs.webkit.org/show_bug.cgi?id=42723

Reviewed by Adam Barth.

Source/WebCore:

Test: fast/files/file-reader-event-listener.html

* fileapi/FileReader.idl:

LayoutTests:

* fast/files/file-reader-event-listener-expected.txt: Added.
* fast/files/file-reader-event-listener.html: Added.

git-svn-id: svn://svn.chromium.org/blink/trunk@104180 bbb929c8-8fbe-4397-9dbb-9b2b20218538