hide SkDevice::config()

TBR=robertphilips

Author: reed@chromium.org

Review URL: https://codereview.chromium.org/302253002
diff --git a/include/gpu/SkGpuDevice.h b/include/gpu/SkGpuDevice.h
index d2df32c..f2a27d7 100644
--- a/include/gpu/SkGpuDevice.h
+++ b/include/gpu/SkGpuDevice.h
@@ -82,7 +82,9 @@
         return NULL == fRenderTarget ? false
                                      : kRGB_565_GrPixelConfig == fRenderTarget->config();
     }
+#ifdef SK_SUPPORT_LEGACY_DEVICE_CONFIG
     virtual SkBitmap::Config config() const SK_OVERRIDE;
+#endif
 
     virtual void clear(SkColor color) SK_OVERRIDE;
     virtual void drawPaint(const SkDraw&, const SkPaint& paint) SK_OVERRIDE;