hide SkBitmap::setConfig

patch from issue 325733002

TBR=scroggo

Author: reed@chromium.org

Review URL: https://codereview.chromium.org/322963002
diff --git a/bench/RectBench.cpp b/bench/RectBench.cpp
index 9013044..a2029e6 100644
--- a/bench/RectBench.cpp
+++ b/bench/RectBench.cpp
@@ -263,8 +263,7 @@
         paint.setStrokeCap(SkPaint::kRound_Cap);
         if (_type == KMaskShader) {
             SkBitmap srcBM;
-            srcBM.setConfig(SkBitmap::kARGB_8888_Config, 10, 1);
-            srcBM.allocPixels();
+            srcBM.allocN32Pixels(10, 1);
             srcBM.eraseColor(0xFF00FF00);
 
             SkShader* s;