Remove multiple GC calls and replace GCController.collect calls with GCController.collectAll

LayoutTests/plugins/refcount-leaks.html

 <script>
   function noop(x) {
   }
 
   function doGC() {
     if (window.GCController) {
-      // GC twice to make sure everything is cleaned up.
-      for (var i = 0; i < 2; i++) {
-        window.GCController.collect();
-      }
+      window.GCController.collectAll();
     }
   }
 
   function runtest() {
     if (window.testRunner)
       testRunner.dumpAsText();
 
 
     var output = document.getElementById("output");
     output.innerHTML = "";
@@ skipping 53 matching lines @@
 an NPAPI Object.<P>
 
 Prints "SUCCESS" on success, "FAILURE" on failure.
 
 <embed name="plug" type="application/x-webkit-test-netscape">
 
 <div id=output>FAILURE</div>
 
 </body>