Hide fields in SkImageInfo

R=rmistry@google.com
TBR=bsalomon

Author: reed@google.com

Review URL: https://codereview.chromium.org/536003002
diff --git a/samplecode/SampleFatBits.cpp b/samplecode/SampleFatBits.cpp
index 6057c68..c300733 100644
--- a/samplecode/SampleFatBits.cpp
+++ b/samplecode/SampleFatBits.cpp
@@ -102,8 +102,7 @@
 
         SkImageInfo info = SkImageInfo::MakeN32Premul(width, height);
         fMinSurface.reset(SkSurface::NewRaster(info));
-        info.fWidth *= zoom;
-        info.fHeight *= zoom;
+        info = info.makeWH(width * zoom, height * zoom);
         fMaxSurface.reset(SkSurface::NewRaster(info));
     }