hide SkBitmap::setConfig

patch from issue 325733002

TBR=scroggo

Author: reed@chromium.org

Review URL: https://codereview.chromium.org/322963002
diff --git a/tests/KtxTest.cpp b/tests/KtxTest.cpp
index ee6a17d..94a4c22 100644
--- a/tests/KtxTest.cpp
+++ b/tests/KtxTest.cpp
@@ -27,9 +27,7 @@
     SkRandom rand(0x1005cbad);
 
     SkBitmap bm8888;
-    bm8888.setConfig(SkBitmap::kARGB_8888_Config, 128, 128);
-
-    bool pixelsAllocated = bm8888.allocPixels();
+    bool pixelsAllocated = bm8888.allocN32Pixels(128, 128);
     REPORTER_ASSERT(reporter, pixelsAllocated);
 
     uint8_t *pixels = reinterpret_cast<uint8_t*>(bm8888.getPixels());