Fix gray png BRD tests

Before my recent CL, these were not run at all (because the decode
color type was gray and the bitmap color type was alpha).
https://skia-review.googlesource.com/c/6088/

Now that these are being run, we should mark the bitmap as
gray so they draw correctly.

BUG=skia:

Change-Id: I9bdfe97671a60da2bcbef55377e1c1b2bd326f8f
Reviewed-on: https://skia-review.googlesource.com/6160
Reviewed-by: Leon Scroggins <scroggo@google.com>
Commit-Queue: Matt Sarett <msarett@google.com>
diff --git a/dm/DMSrcSink.cpp b/dm/DMSrcSink.cpp
index 78e9c55..50b9163 100644
--- a/dm/DMSrcSink.cpp
+++ b/dm/DMSrcSink.cpp
@@ -106,6 +106,16 @@
     return SkBitmapRegionDecoder::Create(encoded, SkBitmapRegionDecoder::kAndroidCodec_Strategy);
 }
 
+static inline void alpha8_to_gray8(SkBitmap* bitmap) {
+    // Android requires kGray8 bitmaps to be tagged as kAlpha8.  Here we convert
+    // them back to kGray8 so our test framework can draw them correctly.
+    if (kAlpha_8_SkColorType == bitmap->info().colorType()) {
+        SkImageInfo newInfo = bitmap->info().makeColorType(kGray_8_SkColorType)
+                                            .makeAlphaType(kOpaque_SkAlphaType);
+        *const_cast<SkImageInfo*>(&bitmap->info()) = newInfo;
+    }
+}
+
 Error BRDSrc::draw(SkCanvas* canvas) const {
     SkColorType colorType = canvas->imageInfo().colorType();
     if (kRGB_565_SkColorType == colorType &&
@@ -148,6 +158,7 @@
                     fSampleSize, colorType, false)) {
                 return "Cannot decode (full) region.";
             }
+            alpha8_to_gray8(&bitmap);
             canvas->drawBitmap(bitmap, 0, 0);
             return "";
         }
@@ -202,6 +213,7 @@
                         return "Cannot decode region.";
                     }
 
+                    alpha8_to_gray8(&bitmap);
                     canvas->drawBitmapRect(bitmap,
                             SkRect::MakeXYWH((SkScalar) scaledBorder, (SkScalar) scaledBorder,
                                     (SkScalar) (subsetWidth / fSampleSize),