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/SampleDither.cpp b/samplecode/SampleDither.cpp
index 38d67ad..57c7613 100644
--- a/samplecode/SampleDither.cpp
+++ b/samplecode/SampleDither.cpp
@@ -70,14 +70,8 @@
 }
 
 static void make_bm(SkBitmap* bm) {
-    bm->setConfig(SkBitmap::kARGB_8888_Config, 100, 100);
-    bm->allocPixels();
-#if 0
-    bm->eraseColor(SK_ColorBLUE);
-    return;
-#else
+    bm->allocN32Pixels(100, 100);
     bm->eraseColor(SK_ColorTRANSPARENT);
-#endif
 
     SkCanvas c(*bm);
     draw_sweep(&c, bm->width(), bm->height(), 0);