hide Config in SkImageDecoder -- use SkColorType instead

patch from issue 334613003

TBR=scroggo

Author: reed@chromium.org

Review URL: https://codereview.chromium.org/334793002
diff --git a/samplecode/SampleSubpixelTranslate.cpp b/samplecode/SampleSubpixelTranslate.cpp
index 686a153..afb31c1 100644
--- a/samplecode/SampleSubpixelTranslate.cpp
+++ b/samplecode/SampleSubpixelTranslate.cpp
@@ -37,8 +37,7 @@
       }
       if (codec) {
           stream.rewind();
-          codec->decode(&stream, &fBM, SkBitmap::kARGB_8888_Config,
-                        SkImageDecoder::kDecodePixels_Mode);
+          codec->decode(&stream, &fBM, kN32_SkColorType, SkImageDecoder::kDecodePixels_Mode);
           SkDELETE(codec);
       } else {
           fBM.allocN32Pixels(1, 1);