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/samplecode/SampleAAClip.cpp b/samplecode/SampleAAClip.cpp
index 5419f68..a1ee67b 100644
--- a/samplecode/SampleAAClip.cpp
+++ b/samplecode/SampleAAClip.cpp
@@ -46,9 +46,7 @@
     clip.copyToMask(&mask);
     SkAutoMaskFreeImage amfi(mask.fImage);
 
-    bm.installPixels(SkImageInfo::MakeA8(mask.fBounds.width(),
-                                         mask.fBounds.height()),
-                     mask.fImage, mask.fRowBytes, NULL, NULL);
+    bm.installMaskPixels(mask);
 
     SkPaint paint;
     canvas->drawBitmap(bm,