Fix Android hit testing in a totally static page.
Our Android hit testing walks up the tree and returns the highest
ancestor that's either (1) a leaf node, or (2) focusable and doesn't
have focusable children.
The bug is that (2) shouldn't include the root element of the tree, which
is indeed focusable. If there are no focusable elements on the page, we don't
want all hit tests to return the root - we want them to return the original
object hit.
BUG=424350
Review URL: https://codereview.chromium.org/
665513002
Cr-Commit-Position: refs/heads/master@{#300007}