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

Original author is "Anish Patankar <anish.p@samsung.com>".
See commmit 273ec5cb, in chromium-ewk repo, master branch.
Reviewed by:  Kangil Han, mohan reddy

Change-Id: Ib71ff1b53f134663dfdd7ac255bfcd62baabface
Signed-off-by: Antonio Gomes <a1.gomes@samsung.com>