add surfaceprops to SkWindow, and 'D' to toggle distancefieldfonts

BUG=skia:

Review URL: https://codereview.chromium.org/631943002
diff --git a/samplecode/SampleApp.h b/samplecode/SampleApp.h
index abb1f24..2e9a11c 100644
--- a/samplecode/SampleApp.h
+++ b/samplecode/SampleApp.h
@@ -118,6 +118,7 @@
     void toggleSlideshow();
     void toggleFPS();
     void showOverview();
+    void toggleDistanceFieldFonts();
 
     GrContext* getGrContext() const { return fDevManager->getGrContext(); }