hide trivial helpers on canvas

BUG=skia:

Change-Id: I42d4ca92897bde5bd8e0575a0104b12b83134cef
Reviewed-on: https://skia-review.googlesource.com/8852
Reviewed-by: Cary Clark <caryclark@google.com>
Commit-Queue: Mike Reed <reed@google.com>
diff --git a/bench/GameBench.cpp b/bench/GameBench.cpp
index 9b811f0..681b823 100644
--- a/bench/GameBench.cpp
+++ b/bench/GameBench.cpp
@@ -104,7 +104,7 @@
         clearPaint.setColor(0xFF000000);
         clearPaint.setAntiAlias(true);
 
-        SkISize size = canvas->getDeviceSize();
+        SkISize size = canvas->getBaseLayerSize();
 
         SkScalar maxTransX, maxTransY;