Revert of Re-landing r170008, removing prefixed Shadow DOM APIs in Element.

Revert of Re-landing r170008, removing prefixed Shadow DOM APIs in Element. (https://codereview.chromium.org/218943003/)

Reason for revert:
Broke OpenAudioFiles/FileManagerBrowserTest again.

http://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%20Tests%20%282%29/builds/22744


Original issue's description:
> Re-landing r170008, removing prefixed Shadow DOM APIs in Element.
> 
> The previous attempt, https://codereview.chromium.org/208503004, was reverted in https://codereview.chromium.org/212303005/.
> The reason of reverting is that there is a JavaScript code uses prefixed Shadow DOM API in the chromium side.
> I've fixed that in https://codereview.chromium.org/214093002/.
> 
> Let me re-land r170008. I hope it won't break anything this time.
> 
> BUG=242153
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=170460

TBR=dglazkov@chromium.org,esprehn@chromium.org,hayato@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=242153
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=170519

[tkent, 2014-04-01 06:50:29]

Created Revert of Re-landing r170008, removing prefixed Shadow DOM APIs in
Element.

[commit-bot: I haz the power, 2014-04-01 06:50:34]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tkent@chromium.org/220123005/1

[commit-bot: I haz the power, 2014-04-01 06:51:06]

Change committed as 170519