WPF - store width/height in local variable upon size change

Do this so it's easier to implement a workaround for #2779

CefSharp.Wpf/ChromiumWebBrowser.cs

@@ -39,6 +39,11 @@ public class ChromiumWebBrowser : Control, IRenderWebBrowser, IWpfWebBrowser
         public const string PartImageName = "PART_image";
         public const string PartPopupImageName = "PART_popupImage";
 
+        /// <summary>
+        /// View Rectangle used by <see cref="GetViewRect"/>
+        /// </summary>
+        private Rect viewRect;
+
         /// <summary>
         /// The source
         /// </summary>
@@ -754,11 +759,6 @@ Rect IRenderWebBrowser.GetViewRect()
         /// <returns>View Rectangle</returns>
         protected virtual Rect GetViewRect()
         {
-            //NOTE: Previous we used Math.Ceiling to round the sizing up, we
-            //now set UseLayoutRounding = true; on the control so the sizes are
-            //already rounded to a whole number for us.
-            var viewRect = new Rect(0, 0, (int)ActualWidth, (int)ActualHeight);
-
             return viewRect;
         }
 
@@ -1856,6 +1856,11 @@ private void OnActualSizeChanged(object sender, SizeChangedEventArgs e)
             // Initialize RenderClientAdapter when WPF has calculated the actual size of current content.
             CreateOffscreenBrowser(e.NewSize);
 
+            //NOTE: Previous we used Math.Ceiling to round the sizing up, we
+            //now set UseLayoutRounding = true; on the control so the sizes are
+            //already rounded to a whole number for us.
+            viewRect = new Rect(0, 0, (int)e.NewSize.Width, (int)e.NewSize.Height);
+
             if (browser != null)
             {
                 browser.GetHost().WasResized();