We need to implement a mapping between JavaScript values and Java objects.

We'd like this mapping to depend on the target (context) type, as defined here:
http://jdk6.java.net/plugin2/liveconnect/#JS_JAVA_CONVERSIONS

Note in the general case we wrap a Javascript object reference using the Java class netscape.javascript.JSObject.

This does not specify exactly how Node values get mapped - they may need some more research and discussion.
(The WebKit Node values aren't JavaScript values directly, but are presumably wrapped by JavaScript objects.)

To start with, we want to have WebPage#executeScript use this mapping.