[Tizen 3.0][EWK API] Change the implementation ewk_view_page_visibility_set

[Tizen 3.0][EWK API] Change the implementation ewk_view_page_visibility_set

Change the implementation of ewk_view_page_visibibility_set means
calling RenderWidgetHostImpl::WasShown or WasHidden functions.
These functions, among others, sends a message to the renderer.
The message handler calls the function OnWasHidden or the function
OnWasShown side renderer.
The current implementation does not differ from the implementation
ewk_view_visibility_set.

Bug: http://web.sec.samsung.net/bugzilla/show_bug.cgi?id=14555.
Reviewed by: Antonio Gomes, Janusz Majnert

Reviewed by: a1.gomes, j.majnert, sns.park

Change-Id: I89e84d92386ded7916b9f0671216b1adc6c99ad2
Signed-off-by: Andrzej Badowski <a.badowski@samsung.com
(cherry picked from commit 87f64fa1041d65d6b48036c5e07af406b56bff4c)