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/bitmapscroll.cpp b/gm/bitmapscroll.cpp
index b14b047..d2b8ca0 100644
--- a/gm/bitmapscroll.cpp
+++ b/gm/bitmapscroll.cpp
@@ -129,7 +129,7 @@
                 // scrollRect() should always return true, even if it's a no-op
                 SkBitmap scrolledBitmap;
                 SkDEBUGCODE(bool copyToReturnValue = )origBitmap.copyTo(
-                    &scrolledBitmap, origBitmap.config());
+                    &scrolledBitmap, origBitmap.colorType());
                 SkASSERT(copyToReturnValue);
                 SkDEBUGCODE(bool scrollRectReturnValue = )scrolledBitmap.scrollRect(
                     subset, scrollX * xMult, scrollY * yMult);