Make SkyElement more classy.

Make SkyElement more classy.

The syntax for implementing a SkyElement is now:

<sky-element name="element-name">
<template>
  <!-- template here -->
</template>
<script>
module.exports = class extends SkyElement {
  attached() {
     // ...
  }
  // .. methods here ..
}.register();
</script>
</sky-element>

The register() static method on SkyElement subclasses calls
document.registerElement() and returns the generated constructor.
It uses the parent <sky-element>'s name attribute to set the name
of the element.

R=rafaelw@chromium.org

Committed: https://chromium.googlesource.com/external/mojo/+/c1d1dd2b46936dadb4277671d13b6ee7ff6d6234

[esprehn, 2014-12-09 22:13:33]

esprehn@chromium.org changed reviewers:
+ ojan@chromium.org, rafaelw@chromium.org

[esprehn, 2014-12-09 22:13:34]

This can't land yet because of
https://code.google.com/p/v8/issues/detail?id=3750

but it shows the syntax change. After thinking for a while this is the framework
sketch I came up with:

http://pastie.org/private/1gsaquglvqna7wxqirdq8q

[rafaelw, 2014-12-10 03:30:55]

lgtm

[esprehn, 2014-12-17 00:28:32]

Committed patchset #2 (id:20001) manually as
c1d1dd2b46936dadb4277671d13b6ee7ff6d6234 (presubmit successful).