Add OpenGL context to Viewer.

tools/viewer/sk_app/Window.cpp

Index: tools/viewer/sk_app/Window.cpp
diff --git a/tools/viewer/sk_app/Window.cpp b/tools/viewer/sk_app/Window.cpp
index 997500c51599b40614f6f80e571dcf051743117e..0a7bcf8a70b75c0f5d61a4dfdb2b36408275e13d 100644
--- a/tools/viewer/sk_app/Window.cpp
+++ b/tools/viewer/sk_app/Window.cpp
@@ -63,7 +63,7 @@ bool Window::onTouch(int owner, InputState state, float x, float y) {
 }
 
 void Window::onPaint() {
-    SkSurface* backbuffer = fWindowContext->getBackbufferSurface();
+    sk_sp<SkSurface> backbuffer = fWindowContext->getBackbufferSurface();
     if (backbuffer) {
         // draw into the canvas of this surface
         SkCanvas* canvas = backbuffer->getCanvas();
@@ -76,7 +76,6 @@ void Window::onPaint() {
     } else {
         // try recreating testcontext
     }
-
 }
 
 void Window::onResize(uint32_t w, uint32_t h) {