Resolving issue #292

- we shouldn't be referencing managed objects in the finalizer

source/SkiaSharp.Views/SkiaSharp.Views.Android/SKCanvasView.cs

@@ -132,8 +132,11 @@ namespace SkiaSharp.Views.Android
 
 		protected override void Dispose(bool disposing)
 		{
+			if (disposing)
+			{
+				FreeBitmap();
+			}
 			base.Dispose(disposing);
-			FreeBitmap();
 		}
 
 		private void FreeBitmap()

source/SkiaSharp.Views/SkiaSharp.Views.Android/SKGLSurfaceViewRenderer.cs

@@ -79,8 +79,11 @@ namespace SkiaSharp.Views.Android
 
 		protected override void Dispose(bool disposing)
 		{
+			if (disposing)
+			{
+				FreeContext();
+			}
 			base.Dispose(disposing);
-			FreeContext();
 		}
 
 		private void FreeContext()

source/SkiaSharp.Views/SkiaSharp.Views.Android/SKSurfaceView.cs

@@ -71,8 +71,11 @@ namespace SkiaSharp.Views.Android
 
 		protected override void Dispose(bool disposing)
 		{
+			if (disposing)
+			{
+				FreeBitmap();
+			}
 			base.Dispose(disposing);
-			FreeBitmap();
 		}
 
 		private void CreateBitmap(int width, int height)