Resolve light-source position/direction when updated

Resolve light-source position/direction when updated

When 'x'/'y'/'z' on fePointLight/feSpotLight, or
'pointsAtX'/'pointsAtY'/'pointsAtZ' on feSpotLight is mutated (animated,
changed through the DOM) and filter primitive units is 'objectBoundingBox',
the new coordinate needs to be resolved against the filter's bounding-box.
Also simplify getting these position/direction attributes of a light-source
element by adding new methods on SVGFELightElement.

BUG=393907
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=178167

[kouhei (in TOK), 2014-07-15 11:30:38]

non-owner lgtm

[Stephen White, 2014-07-15 12:11:12]

On 2014/07/15 11:30:38, kouhei wrote:
> non-owner lgtm

LGTM. Thanks for the quick fix!

[fs, 2014-07-15 12:17:27]

The CQ bit was checked by fs@opera.com

[commit-bot: I haz the power, 2014-07-15 12:18:03]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/fs@opera.com/395813002/1

[commit-bot: I haz the power, 2014-07-15 12:38:34]

Change committed as 178167