[BlackBerry] Add a public function WebPage::isLoading()
https://bugs.webkit.org/show_bug.cgi?id=106751

PR 274392

Patch by Xiaobo Wang <xbwang@torchmobile.com.cn> on 2013-01-13
Reviewed by George Staikos.

Need to get the load state in WebPageClient when resolving PR 274392.

* Api/WebPage.cpp:
(BlackBerry::WebKit::WebPage::isLoading):
(WebKit):
* Api/WebPage.h:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@139582 268f45cc-cd09-0410-ab3c-d52691b4dbfc