Fixes for Element API changes

Fixes for Element API changes

The custom_element analyzer test started failing due to API changes on Element from the last roll.  This should fix.

TBR=jmesserly@google.com,sigmund@google.com

Committed: https://code.google.com/p/dart/source/detail?r=26382

[vsm, 2013-08-20 19:08:59]

Committed patchset #1 manually as r26382 (presubmit successful).

[Siggi Cherem (dart-lang), 2013-08-20 19:14:20]

lgtm

[Jennifer Messerly, 2013-08-20 22:27:08]

I think we can delete this after Pete's custom elements change? And switch to
extending the real HtmlElement

[Siggi Cherem (dart-lang), 2013-08-20 22:37:20]

On 2013/08/20 22:27:08, John Messerly wrote:
> I think we can delete this after Pete's custom elements change? And switch to
> extending the real HtmlElement

that would be really really cool. However, one thing to be careful here is how
does this integrate with the old web_ui, will it continue to work OK?

[Jennifer Messerly, 2013-08-20 22:42:45]

On 2013/08/20 22:37:20, Siggi Cherem (dart-lang) wrote:
> On 2013/08/20 22:27:08, John Messerly wrote:
> > I think we can delete this after Pete's custom elements change? And switch
to
> > extending the real HtmlElement
> 
> that would be really really cool. However, one thing to be careful here is how
> does this integrate with the old web_ui, will it continue to work OK?

hmmm, yeah, that's tricky :)

Can we just change the base class in web_ui?

    class WebComponent extends HtmlElement {
      ... compose children and stuff ...
    }

it's kinda funny because the xtag will be a real DOM node, just not one that is
attached to the document :). But it'll probably work.