Fix Document leak from NodeFilter.

Source/core/dom/NodeIterator.idl

Index: Source/core/dom/NodeIterator.idl
diff --git a/Source/core/dom/NodeIterator.idl b/Source/core/dom/NodeIterator.idl
index d25c3055e887ea28b47657849f856fe185327a77..3a33d79f28e8494d56ef8f3436ccae9d1be3e1bd 100644
--- a/Source/core/dom/NodeIterator.idl
+++ b/Source/core/dom/NodeIterator.idl
@@ -22,7 +22,7 @@
 interface NodeIterator {
     readonly attribute Node root;
     readonly attribute unsigned long whatToShow;
-    readonly attribute NodeFilter filter;
+    [KeepAttributeAliveForGC] readonly attribute NodeFilter filter;

[abarth-chromium, 2013/07/31 06:04:14]

Why is this attribute needed?  Storing the filter on the wrapper should be
sufficient...

[kouhei (in TOK), 2013/07/31 06:21:34]

I'm new to the bindings world so it's very likely I'm just getting this wrong.

The JS callback is used from NodeIterator whenever nextNode()/previousNode() is
called, whether or not attribute filter was referenced from JS.

My understanding is that a new NodeFilter wrapper is created/disposed all the
time when "iterator.filter" is called on JS side. As the NodeFilter wrapper is
where the reference to the JS callback is held, I thought we needed to keep the
NodeFilter's wrapper in NodeIterator's wrapper so it won't be disposed.

[haraken, 2013/07/31 06:46:13]

I think it's a right thing to keep 'filter' alive as long as NodeIterator's
wrapper is alive.

However, maybe you don't need [KeepAttributeAliveForGC], because by default, a
hidden reference is added from NodeIterator's wrapper to readonly attributes
whose type is not Node. (Sorry, the condition under which a hidden reference is
added is extremely complicated. See ShouldKeepAttributeAlive() in the code
generator.)

Would you check that the generated code doesn't change if you remove
[KeepAttributeAliveForGC] ? If it doesn't change, you don't need
[KeepAttributeAliveForGC].

     readonly attribute boolean expandEntityReferences;
     readonly attribute Node referenceNode;
     readonly attribute boolean pointerBeforeReferenceNode;