use SkColorType instead of SkBitmap::Config in samplecode

BUG=skia:
R=reed@google.com

Author: reed@chromium.org

Review URL: https://codereview.chromium.org/169063002

git-svn-id: http://skia.googlecode.com/svn/trunk@13473 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/samplecode/SampleMipMap.cpp b/samplecode/SampleMipMap.cpp
index 3cfeeb7..a9804ac 100644
--- a/samplecode/SampleMipMap.cpp
+++ b/samplecode/SampleMipMap.cpp
@@ -14,8 +14,7 @@
 
 static SkBitmap createBitmap(int n) {
     SkBitmap bitmap;
-    bitmap.setConfig(SkBitmap::kARGB_8888_Config, n, n);
-    bitmap.allocPixels();
+    bitmap.allocN32Pixels(n, n);
     bitmap.eraseColor(SK_ColorTRANSPARENT);
 
     SkCanvas canvas(bitmap);