Per the spec in modules.md the exports property should default to an
empty object. We lazy allocate it so that modules that just replace it
don't create the empty object and then throw it away.
R=abarth@chromium.org
Review URL: https://codereview.chromium.org/872043003
This CL adds basic support for the <import> elements. We're using the same imports
machinery as <link rel="import">, which simplifies this patch substantially.
Currently we support both <link rel="import"> and <import>. Once this CL lands, I'll
update all the existing modules and then we can drop support for
<link rel="import">.
R=ojan@chromium.org
Review URL: https://codereview.chromium.org/681983005
