add new copyTo version to SkBitmap, which takes SkColorType

BUG=skia:
R=scroggo@google.com, halcanary@google.com, bsalomon@google.com

Author: reed@google.com

Review URL: https://codereview.chromium.org/171723007

git-svn-id: http://skia.googlecode.com/svn/trunk@13553 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/utils/mac/SkCreateCGImageRef.cpp b/src/utils/mac/SkCreateCGImageRef.cpp
index 01f2dac..7687c3c 100644
--- a/src/utils/mac/SkCreateCGImageRef.cpp
+++ b/src/utils/mac/SkCreateCGImageRef.cpp
@@ -94,7 +94,7 @@
         copy = new SkBitmap;
         // here we make a ceep copy of the pixels, since CG won't take our
         // 565 directly
-        bm.copyTo(copy, SkBitmap::kARGB_8888_Config);
+        bm.copyTo(copy, kPMColor_SkColorType);
     } else {
         copy = new SkBitmap(bm);
     }