Have htmlcollection-reachable.html force the one GC needed.

third_party/WebKit/LayoutTests/fast/dom/htmlcollection-reachable.html

Index: third_party/WebKit/LayoutTests/fast/dom/htmlcollection-reachable.html
diff --git a/third_party/WebKit/LayoutTests/fast/dom/htmlcollection-reachable.html b/third_party/WebKit/LayoutTests/fast/dom/htmlcollection-reachable.html
index b91c47cd02d2ff03321c1e9b4f576a6e43ca9540..dd02b0fe7298bd009c0081d82ee21788f137f215 100644
--- a/third_party/WebKit/LayoutTests/fast/dom/htmlcollection-reachable.html
+++ b/third_party/WebKit/LayoutTests/fast/dom/htmlcollection-reachable.html
@@ -40,11 +40,13 @@ var collections = [
     'tableRow.cells',
 ];
 
-for (var i = 0; i < collections.length; i++) {
-    var code = collections[i];
-    eval(code).customProperty = i;
-    gc();
-    shouldBe(code + '.customProperty', '' + i);
-}
+// Note: as document.plugins is [ImplementedAs=embeds],
+// use customProperty{i} to ensure uniqueness.
+for (var i = 0; i < collections.length; ++i)
+    eval(collections[i])['customProperty' + i] = i;
 
+gc();
+
+for (var i = 0; i < collections.length; ++i)
+    shouldBe(collections[i] + '.customProperty' + i, '' + i);
 </script>