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

LayoutTests/plugins/multiple-plugins.html

 <script>
   function noop(x) {
   }
 
   function doGC() {
-    if (window.gc) {
-      // GC twice to make sure everything is cleaned up.
-      for (var i = 0; i < 4; i++) {
-        window.gc();
-      }
-    }
+    if (window.GCController)
+      GCController.collectAll();
   }
 
   function runtest() {
     if (window.testRunner)
       testRunner.dumpAsText();
 
     doGC();
 
     var plug1 = document.getElementById("plug1");
     var plug2 = document.getElementById("plug2");
@@ skipping 59 matching lines @@
 
 Prints "SUCCESS" on success, "FAILURE" on failure.
 
 <embed id="plug1" type="application/x-webkit-test-netscape">
 <embed id="plug2" type="application/x-webkit-test-netscape">
 
 <div id=output>FAILURE</div>
 
 </body>