shadow-dom: Remove shadow-trees/test-003.html in favor of reftests.

The tested behavior is covered in two reftests: shadow-root-001.html and
shadow-root-002.html.
shadow-dom: Refine script tests related to ownerDocument property.

This change updates the existing test that checks the ownerDocument property.
The test was split into two files, and renamed to ownerdocument-###.html to
better reflect the test content. Also, the test names were updated so people
can understand what each test is doing.

This change is basically a rewrite of the existing tests, but some tests
were enhanced in hope of achieving better coverage.

ownerdocument-001.html contains basic test cases for ownerDocument property.
ownerdocument-002.html is a test that checks whether the ownerDocument property
is working properly on every HTML5 element.
Merge pull request #218 from yutak/shadow-dom/remove-js-test

shadow-dom: Remove shadow-trees/test-003.html in favor of reftests.
Merge pull request #220 from yutak/shadow-dom/ownerdocument

shadow-dom: Refine script tests related to ownerDocument property.
Merge branch 'master' of https://github.com/w3c/web-platform-tests into submissions/MSakamaki