Add ClearSelection for msw ie and gtk webkit, with a stub for osx webkit. Document and add to unit tests.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/SOC2011_WEBVIEW@68274 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/gtk/webview_webkit.h

@@ -147,6 +147,7 @@ public:
     virtual void SelectAll();
     virtual wxString GetSelectedText();
     virtual wxString GetSelectedSource();
+    virtual void ClearSelection();
 
     /** FIXME: hack to work around signals being received too early */
     bool m_ready;

include/wx/msw/webview_ie.h

@@ -104,6 +104,7 @@ public:
     virtual void DeleteSelection();
     virtual wxString GetSelectedText();
     virtual wxString GetSelectedSource();
+    virtual void ClearSelection();
 
 
     // ---- IE-specific methods

include/wx/osx/webview_webkit.h

@@ -109,6 +109,7 @@ public:
     virtual void SelectAll() {};
     virtual wxString GetSelectedText();
     virtual wxString GetSelectedSource() { return ""; }
+    virtual void ClearSelection() {}
 
     // ---- methods not from the parent (common) interface
     wxString RunScript(const wxString& javascript);

include/wx/webview.h

@@ -290,6 +290,7 @@ public:
     virtual void DeleteSelection() = 0;
     virtual wxString GetSelectedText() = 0;
     virtual wxString GetSelectedSource() = 0;
+    virtual void ClearSelection() = 0;
 
     // TODO:
     //     void EnableJavascript(bool enabled);             // maybe?