Fix Unpremul Index8 tests

dm/DMSrcSink.cpp

Index: dm/DMSrcSink.cpp
diff --git a/dm/DMSrcSink.cpp b/dm/DMSrcSink.cpp
index 7a260e58202659ae8dff19e688cbd584c6284643..9576f69d6708cc7214e87669248dafb1e8a45ca6 100644
--- a/dm/DMSrcSink.cpp
+++ b/dm/DMSrcSink.cpp
@@ -282,6 +282,10 @@ void premultiply_if_necessary(SkBitmap& bitmap) {
             // No need to premultiply kGray or k565 outputs.
             break;
     }
+
+    // In the kIndex_8 case, the canvas won't even try to draw unless we mark the
+    // bitmap as kPremul.
+    bitmap.setAlphaType(kPremul_SkAlphaType);
 }
 
 bool get_decode_info(SkImageInfo* decodeInfo, SkColorType canvasColorType,