[TIZEN][EFL] Expose some HitTestResult APIs through WebHitTestResult.

ChromiumEFL relies on some HitTestResult APIs
being exposed throught WebHitTestResult interface
in order to populate some context menu items.

Namely, the methods are:
* WebURL absoluteMediaURL() const;
* WebString textContent() const;
* WebString titleDisplayString() const;
* bool isSelected() const;

Note that the HitTestResult counterpart of
"titleDisplayString" was removed by [1]. This
CL adds it back.

[1] https://codereview.chromium.org/241713002

BUG=https://crosswalk-project.org/jira/browse/XWALK-2543