replace SkBitmap::Config with SkColorType in gms

add helper installMaskPixels() to SkBitmap

BUG=skia:
R=halcanary@google.com

Author: reed@google.com

Review URL: https://codereview.chromium.org/169913003

git-svn-id: http://skia.googlecode.com/svn/trunk@13482 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gm/blurrect.cpp b/gm/blurrect.cpp
index 3197eb6..52edd6a 100644
--- a/gm/blurrect.cpp
+++ b/gm/blurrect.cpp
@@ -197,8 +197,7 @@
         SkAutoMaskFreeImage amfi(mask.fImage);
 
         SkBitmap bm;
-        bm.setConfig(SkBitmap::kA8_Config, mask.fBounds.width(), mask.fBounds.height());
-        bm.setPixels(mask.fImage);
+        bm.installMaskPixels(mask);
 
         center_x = (canvas_size.fWidth - mask.fBounds.width())/2;
         center_y = (canvas_size.fHeight - mask.fBounds.height())/2;