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/samplecode/SampleDitherBitmap.cpp b/samplecode/SampleDitherBitmap.cpp
index d6d15e9..a3ebafa 100644
--- a/samplecode/SampleDitherBitmap.cpp
+++ b/samplecode/SampleDitherBitmap.cpp
@@ -84,7 +84,7 @@
     DitherBitmapView() {
         fResult = test_pathregion();
         fBM8 = make_bitmap();
-        fBM8.copyTo(&fBM32, SkBitmap::kARGB_8888_Config);
+        fBM8.copyTo(&fBM32, kPMColor_SkColorType);
 
         this->setBGColor(0xFFDDDDDD);
     }