Mark inspector/layer-compositing-reasons.html as timing out

This test will time out after https://codereview.chromium.org/131973020 lands
because content_shell now does a layout after calling the requestAnimationFrame
callbacks, which makes the test environment match the production environment.
Unfortunately, that change causes inspector/layer-compositing-reasons.html to
timeout.  The test appears to rely on the old broken version of
--dump-render-tree's requestAnimationFrame and continually calls
requestAnimationFrame.

BUG=337944
R=esprehn@chromium.org

Review URL: https://codereview.chromium.org/147323002

git-svn-id: svn://svn.chromium.org/blink/trunk@165782 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Make sure the root node of selector queries is a ContainerNode

Make sure the root node of selector queries is a ContainerNode by moving the
querySelector*() methods from the Node class to the ContainerNode class. These
methods are exposed to JS on Document and Element, both of which are
container nodes.

Doing this gets rid of an unnecessary container node check in SelectorQuery
and also enables using the slightly faster firstWithin(ContainerNode) over
firstWithin(Node) traversal method.

R=eseidel, esprehn, adamk

Review URL: https://codereview.chromium.org/138743008

git-svn-id: svn://svn.chromium.org/blink/trunk@165783 bbb929c8-8fbe-4397-9dbb-9b2b20218538