refactor DM::SetupBitmap

Seemed sort of repetitive.

BUG=skia:
R=reed@google.com, mtklein@google.com

Author: mtklein@chromium.org

Review URL: https://codereview.chromium.org/286993005

git-svn-id: http://skia.googlecode.com/svn/trunk@14752 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/dm/DMBenchTask.cpp b/dm/DMBenchTask.cpp
index bcedb96..917e861 100644
--- a/dm/DMBenchTask.cpp
+++ b/dm/DMBenchTask.cpp
@@ -54,7 +54,7 @@
 
 static void draw_raster(SkBenchmark* bench, SkColorType colorType) {
     SkBitmap bitmap;
-    SetupBitmap(colorType, bench, &bitmap);
+    AllocatePixels(colorType, bench->getSize().x(), bench->getSize().y(), &bitmap);
     SkCanvas canvas(bitmap);
 
     bench->preDraw();