use surface in SkView/SampleApp

BUG=skia:
R=bsalomon@google.com, robertphillips@google.com

Author: reed@google.com

Review URL: https://codereview.chromium.org/580073003
diff --git a/samplecode/SampleApp.cpp b/samplecode/SampleApp.cpp
index 9d7e727..08e7240 100644
--- a/samplecode/SampleApp.cpp
+++ b/samplecode/SampleApp.cpp
@@ -271,17 +271,14 @@
         fBackend = kNone_BackEndType;
     }
 
-    virtual SkCanvas* createCanvas(SampleWindow::DeviceType dType,
-                                   SampleWindow* win) {
+    virtual SkSurface* createSurface(SampleWindow::DeviceType dType,
+                                     SampleWindow* win) SK_OVERRIDE {
 #if SK_SUPPORT_GPU
         if (IsGpuDeviceType(dType) && fCurContext) {
-            SkAutoTUnref<SkBaseDevice> device(SkGpuDevice::Create(fCurRenderTarget));
-            return new SkCanvas(device);
-        } else
-#endif
-        {
-            return NULL;
+            return SkSurface::NewRenderTargetDirect(fCurRenderTarget);
         }
+#endif
+        return NULL;
     }
 
     virtual void publishCanvas(SampleWindow::DeviceType dType,