Fixed scrolling in a multiline textbox

Tweaked WindowImpl to only Paint on Expose events

Cairo/Perspex.Cairo/Media/DrawingContext.cs

@@ -51,7 +51,7 @@ namespace Perspex.Cairo.Media
             this.Drawable = drawable;
             this.context = Gdk.CairoHelper.Create(drawable);
             this.CurrentTransform = Matrix.Identity;
-         }
+        }
 
         public Matrix CurrentTransform
         {
@@ -192,7 +192,7 @@ namespace Perspex.Cairo.Media
         {
             var layout = ((FormattedTextImpl)text.PlatformImpl).Layout;
             this.SetBrush(foreground);
-
+            
             this.context.MoveTo(origin.X, origin.Y);
             Pango.CairoHelper.ShowLayout(this.context, layout);
         }

Cairo/Perspex.Cairo/Media/FormattedTextImpl.cs

@@ -37,15 +37,17 @@ namespace Perspex.Cairo.Media
             this.Layout.Alignment = textAlignment.ToCairo();
         }
 
+        private Size size;
         public Size Constraint
         {
             get
             {
-                return new Size(this.Layout.Width, double.PositiveInfinity);
+                return size;
             }
 
             set
             {
+                this.size = value;
                 this.Layout.Width = Pango.Units.FromDouble(value.Width);
             }
         }

Gtk/Perspex.Gtk/WindowImpl.cs

@@ -161,7 +161,11 @@ namespace Perspex.Gtk
 
         protected override bool OnExposeEvent(Gdk.EventExpose evnt)
         {
-            this.Paint(evnt.Area.ToPerspex(), this.GetHandle(evnt.Window));
+            if (evnt.Type == Gdk.EventType.Expose)
+            {
+                this.Paint(evnt.Area.ToPerspex(), this.GetHandle(evnt.Window));
+            }
+
             return true;
         }