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/gm/copyTo4444.cpp b/gm/copyTo4444.cpp
index 4efe00b..7e2c279 100644
--- a/gm/copyTo4444.cpp
+++ b/gm/copyTo4444.cpp
@@ -40,7 +40,7 @@
             return;
         }
         canvas->drawBitmap(bm, 0, 0);
-        SkAssertResult(bm.copyTo(&bm4444, SkBitmap::kARGB_4444_Config));
+        SkAssertResult(bm.copyTo(&bm4444, kARGB_4444_SkColorType));
         canvas->drawBitmap(bm4444, SkIntToScalar(bm.width()), 0);
     }