Use tighter typing for Document::ownerElement() return value

Use tighter typing for Document::ownerElement() return value

Use tighter typing for Document::ownerElement() return value. It returns an
HTMLFrameOwnerElement* but a lot of callers assign it to an Element* variable.

This gets rid of a few unnecessary type checks and avoids an unnecessary
isHTMLElement() check in isHTMLFrameElementBase() in several cases.

R=adamk@chromium.org, rob.buis@samsung.com

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=180400

[adamk, 2014-08-16 00:51:23]

lgtm

[Inactive, 2014-08-16 00:52:14]

The CQ bit was checked by ch.dumez@samsung.com

[commit-bot: I haz the power, 2014-08-16 00:52:39]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ch.dumez@samsung.com/476223003/1

[commit-bot: I haz the power, 2014-08-16 01:39:37]

Committed patchset #1 (1) as 180400