[Resource Timing] Feedback on the IDL

I took a pass through the IDL for Resource Timing. I have a few suggestions:

1. For the PerformanceResourceTimingList, I think we should copy the IDL
from another list type. An example is StyleSheetList from here:

http://www.w3.org/TR/1999/WD-DOM-Level-2-19990923/stylesheets.html

Namely, we should have a function called item() that returns the given entry
in the list.

2. For onbufferfull, I think the name should include Resource Timing
somewhere, so it matches the functions.

Alternatively, have we considered putting all of the Resource Timing
functions in their own namespace under performance? It would cut down on the
verbosity.

3. For getResourceTimingsByLocation, I think we should use a DOMString for
the argument instead of a Location. That seems to be how other places pass
in URLs, like window.open(). The variable name should be url instead of
location too.

James