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/tools/CopyTilesRenderer.cpp b/tools/CopyTilesRenderer.cpp
index d3f266b..1298d43 100644
--- a/tools/CopyTilesRenderer.cpp
+++ b/tools/CopyTilesRenderer.cpp
@@ -70,7 +70,7 @@
                                 dst.pixelRef()->readPixels(&copy, &subset);
                             } else {
 #endif
-                                dst.copyTo(&copy, dst.config());
+                                dst.copyTo(&copy);
 #if SK_SUPPORT_GPU
                             }
 #endif