Use new Traversal<SVG*Element> API more in SVG code

Use new Traversal<SVG*Element> API more in SVG code

Use new Traversal<SVG*Element> API more in SVG code. This makes the code a
bit shorter / simpler.

This CL also defines new DEFINE_ELEMENT_TYPE_CASTS*() macros that do the same
as DEFINE_NODE_TYPE_CASTS*() macros but also provide a template specialization
of isElementOfType<>() so that the Traversal<> API also works for these
Element types. For most types, those helpers are automatically generated from
SVGTagNames.in and those require no additional work.

R=eseidel, pdr
BUG=346733
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=168790

[eseidel, 2014-03-08 21:27:54]

lgtm

[commit-bot: I haz the power, 2014-03-08 21:28:00]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/ch.dumez@samsung.com/191963002/1

[commit-bot: I haz the power, 2014-03-08 22:05:39]

Change committed as 168790