This has the following implications:

 - There's no createElement() function any more. If you want to create
   an element from script, you have to use its constructor.

 - There's no async element registration. The parser will block until
   all the imports are imported when you use a tag name of a custom
   element that hasn't been registered yet, in case one of the imports
   defines it.

 - If you try to construct a non-registered element in markup, it
   turns into an <error> element.

 - <div>, <span>, and <error> are new built-in elements.

R=esprehn@chromium.org

Review URL: https://codereview.chromium.org/695423004

Previously we were using string concatenation to build up the directory
listing. Now we fetch some JSON from the server and use data binding to inflate
a directory listing.

This exmaple doesn't work yet because we're missing support for
template@repeat, but hopefully we'll get that soon.

Also, added support for setRequestHeader to XMLHttpRequest.

R=rafaelw@chromium.org

Review URL: https://codereview.chromium.org/688413005

This CL is just a search-and-replace.

R=esprehn@chromium.org

Review URL: https://codereview.chromium.org/694423002

exported and reexported, rename 'interface' to 'class' in the IDL, add
constructors to all registered elements

R=esprehn@chromium.org

Review URL: https://codereview.chromium.org/695043002

BUG=
R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/698653002

R=esprehn@chromium.org

Review URL: https://codereview.chromium.org/694613002

Review URL: https://codereview.chromium.org/689763003

Review URL: https://codereview.chromium.org/692563003

Docs: Fix the script in the example to actually clone the template contents, not the template element itself.

Review URL: https://codereview.chromium.org/680673002

I had to also register for the text/plain mime-type
which turned out to be harder than expected.
Mostly due to my confusion with mojo_shell
using last-argument-wins argument parsing.

R=ianh@google.com

Review URL: https://codereview.chromium.org/672363002

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/677513002