Add SkEncodedInfo to report properties of encoded image data

src/codec/SkGifCodec.cpp

Index: src/codec/SkGifCodec.cpp
diff --git a/src/codec/SkGifCodec.cpp b/src/codec/SkGifCodec.cpp
index 2233c66c19f5ca81ac002f2f46bce377fc7e80d1..3304a5386c93db2e7641d9ad1e172c2ea2be49ef 100644
--- a/src/codec/SkGifCodec.cpp
+++ b/src/codec/SkGifCodec.cpp
@@ -199,24 +199,22 @@ bool SkGifCodec::ReadHeader(SkStream* stream, SkCodec** codecOut, GifFileType**
         }
         bool frameIsSubset = (size != frameRect.size());
 
-        // Determine the recommended alpha type.  The transIndex might be valid if it less
+        // Determine the encoded alpha type.  The transIndex might be valid if it less
         // than 256.  We are not certain that the index is valid until we process the color
         // table, since some gifs have color tables with less than 256 colors.  If
         // there might be a valid transparent index, we must indicate that the image has
         // alpha.
-        // In the case where we must support alpha, we have the option to set the
-        // suggested alpha type to kPremul or kUnpremul.  Both are valid since the alpha
-        // component will always be 0xFF or the entire 32-bit pixel will be set to zero.
-        // We prefer kPremul because we support kPremul, and it is more efficient to use
-        // kPremul directly even when kUnpremul is supported.
-        SkAlphaType alphaType = (transIndex < 256) ? kPremul_SkAlphaType : kOpaque_SkAlphaType;
+        // In the case where we must support alpha, we indicate kBinary, since every
+        // pixel will either be fully opaque or fully transparent.
+        SkEncodedInfo::Alpha alpha = (transIndex < 256) ? SkEncodedInfo::kBinary_Alpha :
+                SkEncodedInfo::kOpaque_Alpha;
 
         // Return the codec
-        // kIndex is the most natural color type for gifs, so we set this as
-        // the default.
-        SkImageInfo imageInfo = SkImageInfo::Make(size.width(), size.height(), kIndex_8_SkColorType,
-                alphaType);
-        *codecOut = new SkGifCodec(imageInfo, streamDeleter.release(), gif.release(), transIndex,
+        // Use kPalette since Gifs are encoded with a color table.
+        // Use 8-bits per component, since this is the output we get from giflib.
+        // FIXME: Gifs can actually be encoded with 4-bits per pixel.  Can we support this?
+        SkEncodedInfo info = SkEncodedInfo::Make(size, SkEncodedInfo::kPalette_Color, alpha, 8);
+        *codecOut = new SkGifCodec(info, streamDeleter.release(), gif.release(), transIndex,
                 frameRect, frameIsSubset);
     } else {
         SkASSERT(nullptr != gifOut);
@@ -239,9 +237,9 @@ SkCodec* SkGifCodec::NewFromStream(SkStream* stream) {
     return nullptr;
 }
 
-SkGifCodec::SkGifCodec(const SkImageInfo& srcInfo, SkStream* stream, GifFileType* gif,
+SkGifCodec::SkGifCodec(const SkEncodedInfo& info, SkStream* stream, GifFileType* gif,
         uint32_t transIndex, const SkIRect& frameRect, bool frameIsSubset)
-    : INHERITED(srcInfo, stream)
+    : INHERITED(info, stream)
     , fGif(gif)
     , fSrcBuffer(new uint8_t[this->getInfo().width()])
     , fFrameRect(frameRect)