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

LayoutTests/svg/animations/smil-leak-element-instances.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 18 matching lines @@
 
     use.appendChild(anim);
 
     return use;
 }
 
 function cleanup() {
     // Collect garbage before recording starting live node count, in case there are live elements from previous tests.
     // FIXME: Unclear why two calls to collect() are required, see crbug.com/307614
     GCController.collect();
     GCController.collect();

[haraken, 2014/03/26 03:39:03]

What happens if we call GCController.collect() more times?

     var originalLiveElements = internals.numberOfLiveNodes();
 
     while (g.hasChildNodes())
         g.removeChild(g.lastChild);
 
     GCController.collect();

[haraken, 2014/03/26 03:39:03]

Ditto.

 
-    // FIXME: Why is this 400 instead of 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() {
     // Hold a reference to rect.x.baseVal on the root instance.
     xBaseVal = document.getElementById("rect").x.baseVal;
@@ skipping 11 matching lines @@
     } else {
         log("This test only works when run with the testRunner, GCController, and internals available.");
         return;
     }
 
     setTimeout(startTest, 0);
 }
 ]]>
 </script>
 </svg>