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/SampleLayerMask.cpp b/samplecode/SampleLayerMask.cpp
index 33c06d1..b3bbac6 100644
--- a/samplecode/SampleLayerMask.cpp
+++ b/samplecode/SampleLayerMask.cpp
@@ -36,8 +36,7 @@
             SkBitmap mask;
             int w = SkScalarRoundToInt(r.width());
             int h = SkScalarRoundToInt(r.height());
-            mask.setConfig(SkBitmap::kARGB_8888_Config, w, h);
-            mask.allocPixels();
+            mask.allocN32Pixels(w, h);
             mask.eraseColor(SK_ColorTRANSPARENT);
             SkCanvas c(mask);
             SkRect bounds = r;