Make manual isSVG*Element() helpers as efficient as the generated ones

Make manual isSVG*Element() helpers as efficient as the generated ones by
introducing a DEFINE_SVGELEMENT_TYPE_CASTS_WITH_FUNCTION() macro, similarly
to the DEFINE_HTMLELEMENT_TYPE_CASTS_WITH_FUNCTION(). This new macro is
used instead of DEFINE_ELEMENT_TYPE_CASTS_WITH_FUNCTION() for SVG types so
that the isSVG*Element() helpers leverage the faster
SVGElement::hasTagName(SVGQualifiedName) when possible (i.e. when the input
is an SVGElement*).

This is a follow-up to:
https://src.chromium.org/viewvc/blink?view=rev&revision=178540

R=pdr@chromium.org, abarth@chromium.org

Review URL: https://codereview.chromium.org/403343005

git-svn-id: svn://svn.chromium.org/blink/trunk@178580 bbb929c8-8fbe-4397-9dbb-9b2b20218538