Add beginEvent/endEvent listeners via the onbegin/onend attributes.

LayoutTests/svg/animations/onend.svg

Index: LayoutTests/svg/animations/onend.svg
diff --git a/LayoutTests/svg/animations/begin-event.svg b/LayoutTests/svg/animations/onend.svg
similarity index 80%
copy from LayoutTests/svg/animations/begin-event.svg
copy to LayoutTests/svg/animations/onend.svg
index bbe6e4ccdbd751a0827b8e2a8c6a0340e9dfb4cf..1dacbc683fd71d6dbbe071464aacd7e08a91d359 100644
--- a/LayoutTests/svg/animations/begin-event.svg
+++ b/LayoutTests/svg/animations/onend.svg
@@ -2,8 +2,8 @@
 <!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1 Tiny//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11-tiny.dtd">
 <svg onload="loaded()" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
   <rect x="0" y="0" width="0" height="100" fill="green">
-    <animate id="anim" attributeName="visibility" to="visible" begin="0s" end="2s" fill="freeze"/>
-    <set attributeName="width" to="100" begin="anim.beginEvent" />
+    <animate id="anim" attributeName="visibility" to="visible" begin="0s" end="2s" fill="freeze" onend="document.getElementById('anim2').beginElement()"/>
+    <set id="anim2" attributeName="width" to="100" begin="indefinite" />
   </rect>
   <script>
     if (window.testRunner)