shadow-dom: Update a test for shadow root's accessors.

Tests in the original file, test-006.html, are rewritten and are now in
two new files: dom-tree-accessors-002.html and selectors-api-002.html.
Merge pull request #237 from yutak/shadow-dom/shadow-root-accessors

shadow-dom: Update a test for shadow root's accessors.
sync with DOM
Merge pull request #244 from annevk/patch-2

sync with DOM
Add a test for empty names in HTMLCollection in DOM.
Add more whitespace between tests.
Merge pull request #245 from Ms2ger/HTMLCollection-empty-name

Add a test for empty names in HTMLCollection in DOM.
whitespace
add OfflineAudioContext to vender prefix
file rename
gain node test
remove interface test helper. We'll use WebIDL now.
refactor bufferLoader to use decodeAudioData
remove unused helpers and add assert_array_approx_equals
add assertions
Add visibility test for hidden parent with visible children

In an overflow context where overflow is hidden, absolutely positioned
child elements are still visible in the browser.  The parent container
is by webdriver also considered visible for the reason of
interactability.
add a longer timeout to the test
remove old assert helpers, they're in testharness.js now.
Merge pull request #247 from andreastt/andreastt/overflow_parent_visible_with_absolute_children

Add visibility test for hidden parent with visible children