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

LayoutTests/plugins/refcount-leaks.html

Index: LayoutTests/plugins/refcount-leaks.html
diff --git a/LayoutTests/plugins/refcount-leaks.html b/LayoutTests/plugins/refcount-leaks.html
index 69f6ee0a5af5757d24d1f55e0954f759cb140d91..0980fe1b275022a35f3739c7ced425f67bdc1bb6 100644
--- a/LayoutTests/plugins/refcount-leaks.html
+++ b/LayoutTests/plugins/refcount-leaks.html
@@ -4,10 +4,7 @@
 
   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();
     }
   }