Use DEFINE_NODE_TYPE_CASTS instead of using manual toHTMLFooElement()

Use DEFINE_NODE_TYPE_CASTS instead of using manual toHTMLFooElement()

Replace manual toHTMLFooElement() with DEFINE_NODE_TYPE_CASTS(). It supports more
various helper functions as well as we can use it easily. However, this cl only can
cover toHTMLFooElement() except for non-support toHTMLFooElement().

BUG=N/A

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=159740

[gyuyoung-inactive, 2013-10-14 02:17:53]

Add tkent.

[tkent, 2013-10-16 00:38:43]

lgtm

Thanks!

[commit-bot: I haz the power, 2013-10-16 00:39:01]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/gyuyoung.kim@samsung.com/27142002/1

[commit-bot: I haz the power, 2013-10-16 09:52:23]

Change committed as 159740