[SVG] call GCController.collectAll on SVG leak tests to address Oilpan flakiness.

LayoutTests/svg/animations/smil-leak-element-instances-noBaseValRef.svg

 <svg id="svg" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" onload="load()">
 <defs>
     <rect id="rect" width="100" height="100" />
 </defs>
 <g id="g"/>
 <text x="50" y="50" id="log"/>
 <script id="script">
 <![CDATA[
 
 var g = document.getElementById("g");
@@ skipping 26 matching lines @@
     // FIXME: Unclear why two calls to collect() are required, see crbug.com/307614
     GCController.collect();
     GCController.collect();
     var originalLiveElements = internals.numberOfLiveNodes();
 
     while (g.hasChildNodes())
         g.removeChild(g.lastChild);
 
     GCController.collect();
 
-    // FIXME: Why 400 and not 200?
+    // This is 400 instead of 200 as it creates shadow tree elements.
     var liveDelta = originalLiveElements - internals.numberOfLiveNodes() - 400;
-    if (liveDelta == 0)
+    if (liveDelta <= 0)
         log("PASS");
     else
         log("FAIL: " + liveDelta + " extra live node(s)");
 
     testRunner.notifyDone();
 }
 
 function startTest() {
     for (var i = 0; i < 100; i++)
         g.appendChild(createAnimatedRectInstance());
 
     setTimeout(cleanup, 0);
 }
 
 function load() {
     if (window.testRunner && window.GCController && window.internals) {
         testRunner.dumpAsText();
         testRunner.waitUntilDone();
     } else {
         log("This test only works when run with the testRunner, GCController, and internals available.");
         return;
     }
 
     setTimeout(startTest, 0);
 }
 ]]>
 </script>
 </svg>