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/bitmapfilters.cpp b/gm/bitmapfilters.cpp
index 5856f87..7addf25 100644
--- a/gm/bitmapfilters.cpp
+++ b/gm/bitmapfilters.cpp
@@ -20,8 +20,9 @@
     }
     SkColorTable* ctable = new SkColorTable(colorsPM, 4);
 
-    bm->setConfig(SkBitmap::kIndex8_Config, 2, 2);
-    bm->allocPixels(ctable);
+    bm->allocPixels(SkImageInfo::Make(2, 2, kIndex_8_SkColorType,
+                                      kPremul_SkAlphaType),
+                    NULL, ctable);
     ctable->unref();
 
     *bm->getAddr8(0, 0) = 0;