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/gmmain.cpp b/gm/gmmain.cpp
index c52c5d8..662e981 100644
--- a/gm/gmmain.cpp
+++ b/gm/gmmain.cpp
@@ -293,7 +293,7 @@
         // from this method, we should be able to get rid of the
         // transformation to 8888 format also.
         SkBitmap copy;
-        bitmap.copyTo(&copy, SkBitmap::kARGB_8888_Config);
+        bitmap.copyTo(&copy, kPMColor_SkColorType);
         if (!SkImageEncoder::EncodeFile(path.c_str(), copy,
                                         SkImageEncoder::kPNG_Type,
                                         100)) {