Add NavStateChanged EventHandler to WPF control

Add NavStateChanged to IWebBrowser
Update xml comment
Add stub to Offscreen ChromiumWebBrowser

Author: amaitland

CefSharp.OffScreen/ChromiumWebBrowser.cs

@@ -184,6 +184,7 @@ public Task<Bitmap> ScreenshotAsync()
         public event EventHandler<ConsoleMessageEventArgs> ConsoleMessage;
         public event EventHandler BrowserInitialized;
         public event EventHandler<StatusMessageEventArgs> StatusMessage;
+        public event EventHandler<NavStateChangedEventArgs> NavStateChanged;
 
         public void ShowDevTools()
         {

CefSharp.Wpf/ChromiumWebBrowser.cs

@@ -57,6 +57,7 @@ public class ChromiumWebBrowser : ContentControl, IRenderWebBrowser, IWpfWebBrow
         public event EventHandler<FrameLoadStartEventArgs> FrameLoadStart;
         public event EventHandler<FrameLoadEndEventArgs> FrameLoadEnd;
         public event EventHandler<LoadErrorEventArgs> LoadError;
+        public event EventHandler<NavStateChangedEventArgs> NavStateChanged;
 
         public ICommand BackCommand { get; private set; }
         public ICommand ForwardCommand { get; private set; }
@@ -677,6 +678,12 @@ void IWebBrowserInternal.SetNavState(bool canGoBack, bool canGoForward, bool can
 
                 RaiseCommandsCanExecuteChanged();
             });
+
+            var handler = NavStateChanged;
+            if (handler != null)
+            {
+                handler(this, new NavStateChangedEventArgs(canGoBack, canGoForward, canReload));
+            }
         }
 
         private void RaiseCommandsCanExecuteChanged()

CefSharp/IWebBrowser.cs

@@ -39,6 +39,13 @@ public interface IWebBrowser : IDisposable
         /// </summary>
         event EventHandler<LoadErrorEventArgs> LoadError;
 
+        /// <summary>
+        /// Event handler that will get called when the Navigation state has changed (Maps to OnLoadingStateChange in Cef).
+        /// This event will be fired twice. Once when loading is initiated either programmatically or
+        /// by user action, and once when loading is terminated due to completion, cancellation of failure. 
+        /// </summary>
+        event EventHandler<NavStateChangedEventArgs> NavStateChanged;
+
         /// <summary>
         /// Loads the specified URL.
         /// </summary>

CefSharp/IWinFormsWebBrowser.cs

@@ -10,7 +10,6 @@ namespace CefSharp
     // so the dependency would go the wrong way... Has to be here for the time being.
     public interface IWinFormsWebBrowser : IWebBrowser
     {
-        event EventHandler<NavStateChangedEventArgs> NavStateChanged;
         event EventHandler<TitleChangedEventArgs> TitleChanged;
         event EventHandler<AddressChangedEventArgs> AddressChanged;
         void Undo();