Merge wxWebView JavaScript improvements branch

This is a squashed commit of the SOC2017_WEBVIEW_JS branch from
https://github.com/joseeloren/wxWidgets.git

Closes https://github.com/wxWidgets/wxWidgets/pull/538

include/wx/gtk/private/webkit.h

@@ -0,0 +1,57 @@
+///////////////////////////////////////////////////////////////////////////////
+// Name:        wx/gtk/private/webkit.h
+// Purpose:     wxWebKitGtk RAII wrappers declaration
+// Author:      Jose Lorenzo
+// Created:     2017-08-21
+// Copyright:   (c) 2017 Jose Lorenzo <josee.loren@gmail.com>
+// Licence:     wxWindows licence
+///////////////////////////////////////////////////////////////////////////////
+
+#ifndef _WX_GTK_PRIVATE_WEBKIT_H_
+#define _WX_GTK_PRIVATE_WEBKIT_H_
+
+#include <webkit2/webkit2.h>
+#include <JavaScriptCore/JSStringRef.h>
+#include <wx/buffer.h>
+
+// ----------------------------------------------------------------------------
+// Convenience class for WebKitJavascriptResult on scope exit automatically
+// ----------------------------------------------------------------------------
+
+class wxWebKitJavascriptResult
+{
+public:
+    explicit wxWebKitJavascriptResult(WebKitJavascriptResult *r) : m_jsresult(r) { }
+    ~wxWebKitJavascriptResult() { webkit_javascript_result_unref (m_jsresult); }
+
+    operator WebKitJavascriptResult *() const { return m_jsresult; }
+
+private:
+    WebKitJavascriptResult *m_jsresult;
+
+    wxDECLARE_NO_COPY_CLASS(wxWebKitJavascriptResult);
+};
+
+class wxJSStringRef
+{
+public:
+    explicit wxJSStringRef(JSStringRef r) : m_jssref(r) { }
+    ~wxJSStringRef() { JSStringRelease (m_jssref); }
+
+    const wxString ToWxString()
+    {
+        size_t length = JSStringGetMaximumUTF8CStringSize(m_jssref);
+        wxCharBuffer str(length);
+
+        JSStringGetUTF8CString(m_jssref, str.data(), length);
+
+        return wxString::FromUTF8(str);
+    }
+
+private:
+    JSStringRef m_jssref;
+
+    wxDECLARE_NO_COPY_CLASS(wxJSStringRef);
+};
+
+#endif // _WX_GTK_PRIVATE_WEBKIT_H_