Invalidate SVG filter display items on subtree modification

LayoutTests/svg/filters/filter-refresh.svg

 <svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink"
   style="width:300px;height:400px" onload="runRepaintAndPixelTest()">
 
 <script xlink:href="../../fast/repaint/resources/text-based-repaint.js"></script>
 <!-- This tests filters failing to refresh after the initial rendering
 (https://bugs.webkit.org/show_bug.cgi?id=53088).
 There should be no red squares in the output. -->
 
 <defs>
 <filter id="simple" x="0" y="0">
   <feOffset in="SourceGraphic" dx="0" dy="0" />
 </filter>
 
 <filter id="animated" x="0" y="0">
-  <animate attributeName="x" from="0" to="0" dur="0.05s"/>
+  <set attributeName="x" to="0" />

[pdr., 2015/05/20 21:09:27]

Now that we are tracking invalidations, this flakiness caused by this animation
was exposed (this caused the debug failure). This change shouldn't actually
change this test.

[fs, 2015/05/20 21:57:08]

Acknowledged.

   <feOffset in="SourceGraphic" dx="0" dy="0" />
 </filter>
 
 <filter id="toGreen" x="0" y="0">
   <feComponentTransfer>
     <feFuncG type="linear" intercept="0.25" slope="0"/>
     <feFuncR type="linear" intercept="0" slope="0"/>
     <feFuncB type="linear" intercept="0" slope="0"/>
   </feComponentTransfer>
 </filter>
@@ skipping 81 matching lines @@
     function repaintTest() {
       for (var i=0; i<elements.length; ++i) {
         elements[i].setAttribute('fill', 'green');
       }
 
       document.getElementById('filtered').setAttribute('filter', 'url(#toGreen)');
     }
 ]]></script>
 
 </svg>