Support decoding PNG to 565.

src/codec/SkCodec_libpng.cpp

Index: src/codec/SkCodec_libpng.cpp
diff --git a/src/codec/SkCodec_libpng.cpp b/src/codec/SkCodec_libpng.cpp
index d29ca8a2a300bbc2635a93c05b6b8c33d1fca220..b2706ba1baf13153451a0a5a88594663a4021850 100644
--- a/src/codec/SkCodec_libpng.cpp
+++ b/src/codec/SkCodec_libpng.cpp
@@ -419,6 +419,8 @@ static bool conversion_possible(const SkImageInfo& dst, const SkImageInfo& src)
     switch (dst.colorType()) {
         case kN32_SkColorType:
             return true;
+        case kRGB_565_SkColorType:
+            return src.alphaType() == kOpaque_SkAlphaType;
         default:
             return dst.colorType() == src.colorType();
     }