hide SkBitmap::setConfig

patch from issue 325733002

TBR=scroggo

Author: reed@chromium.org

Review URL: https://codereview.chromium.org/322963002
diff --git a/bench/TileBench.cpp b/bench/TileBench.cpp
index 9a9e27e..12c9629 100644
--- a/bench/TileBench.cpp
+++ b/bench/TileBench.cpp
@@ -48,9 +48,7 @@
         , fDoScale(doScale) {
         SkBitmap bm;
 
-        bm.setConfig(SkBitmap::kARGB_8888_Config, kWidth, kHeight, 0,
-                     kOpaque_SkAlphaType);
-        bm.allocPixels();
+        bm.allocN32Pixels(kWidth, kHeight, true);
         bm.eraseColor(SK_ColorWHITE);
 
         create_gradient(&bm);