Add SVGTests attrs to SVGSMILElement to support SVGDiscardElement

Add SVGTests attrs to SVGSMILElement to support SVGDiscardElement

Before this CL, SVGAnimationElement derived SVGTests.
However, given that SVGDiscardElement, which also derives SVGSMILElement
need SVGTests support too, this CL changes SVGTests to be inherited in
SVGSMILElement.

Before:
class SVGSMILElement {}
class SVGAnimationElement : SVGSMILElement, SVGTests {}
class SVGDiscardElement : SVGSMILElement {}

After:
class SVGSMILElement : SVGTests {}
class SVGAnimationElement : SVGSMILElement {}
class SVGDiscardElement : SVGSMILElement {}

BUG=397991
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=179107

[kouhei (in TOK), 2014-07-29 03:45:32]

Would you take a look?
fs: This modifies the hierarchy as we discussed in
https://codereview.chromium.org/424733002/

[fs, 2014-07-29 08:22:50]

LGTM

[kouhei (in TOK), 2014-07-29 08:23:39]

The CQ bit was checked by kouhei@chromium.org

[commit-bot: I haz the power, 2014-07-29 08:24:44]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/kouhei@chromium.org/427613006/1

[commit-bot: I haz the power, 2014-07-29 08:38:22]

Change committed as 179107