Text projected into an anchor should be clickable

We should use NodeRenderingTraversal::parent instead of parentNode
or parentOrShadowHostNode when walking up from Text nodes to find the
hit target in EventHandler, or when finding the nearest enclosing link
in Node::enclosingLinkEventParentOrSelf().

In general there's a lot of hairy stuff in EventHandler and
HitTestResult where it's not clear if we should be using
NodeRenderingTraversal or regular DOM traversals. We need to discuss
the correct behavior of the platform here. The polymer team keeps
asking this question too.

Clearly in this case it's better to allow the text to be clickable
though.

BUG=314488

Review URL: https://codereview.chromium.org/299443008

git-svn-id: svn://svn.chromium.org/blink/trunk@174586 bbb929c8-8fbe-4397-9dbb-9b2b20218538