Fix touch events on SVG elements

This patch is a partial merge of http://trac.webkit.org/changeset/160668
by Daniel Bates <dbates@webkit.org>.

This patch adds support for touch events on SVG elements, and adds a
test to prove it works (this failed before this patch). This patch also
contains a small fix to SVGAElement::willRespondToMouseClickEvents to
make it match HTMLAnchorElement::willRespondToMouseClickEvents().

BUG=328954

Review URL: https://codereview.chromium.org/111723009

git-svn-id: svn://svn.chromium.org/blink/trunk@164055 bbb929c8-8fbe-4397-9dbb-9b2b20218538