Ignore remote files during build

[FredKSchott]

Fixes #10

/cc @justinfagnani @filipproch

[justinfagnani]

"remote" should include URLs on the same host that are outside the application root, but first we need to add support for application roots. Can you add a TODO here for that?

[FredKSchott]

Oh good call. Yea that's a much more complicated issue, I'll add the TODO.

[justinfagnani]

LGTM with small comments

[jpincas]

Is this working?

function isDependencyExternal(url: string) {
  // TODO(fks) 08-01-2016: Add additional check for files on current hostname
  // but external to this application root. Ignore them.
  return parseUrl(url).protocol !== null || url.startsWith('//');
}

Once of my imports is:

<link rel="import" href="http://localhost:3000/admin-panel/polymer-imports.html">

and it is causing a build error. Doesn't seem to matter whether I start the href with the protocol or '//'.

[jpincas]

OK - looking through the code a bit more closely I can see that ignoring external dependencies only applies to script and style dependencies. Is there a particular reason for this? I am importing a dynamically rendered html file from an external server which contains a lot of setup information as behaviors. It works perfectly with 'polymer serve' and seems like a good architecture. Is it unwise for some reason?