PolymerLabs/x-meta — pull request #1 by raggi (2014-05-21 18:52:47+00:00)
Title: support extended elements, supporting is attribute

makes drag and drop work for extended elements in designer. this isn't noticable
for elements that extend other polymer-elements, but when extending native
elements the native tag is not registered.

debugged with @bokor and @adamtanner