Set sRGB flag for PNGs with an sRGB chunk

src/codec/SkPngCodec.cpp

Index: src/codec/SkPngCodec.cpp
diff --git a/src/codec/SkPngCodec.cpp b/src/codec/SkPngCodec.cpp
index 232373c04407c63c2b391c148a7053db9e9d62e9..656df7da0b837f868a4b32732f3d972ae606584d 100644
--- a/src/codec/SkPngCodec.cpp
+++ b/src/codec/SkPngCodec.cpp
@@ -328,10 +328,13 @@ static bool read_header(SkStream* stream, SkPngChunkReader* chunkReader,
         *numberPassesPtr = numberPasses;
     }
 
-    // FIXME: Also need to check for sRGB ( https://bug.skia.org/3471 ).
+    SkColorProfileType profileType = kLinear_SkColorProfileType;
+    if (png_get_valid(png_ptr, info_ptr, PNG_INFO_sRGB)) {
+        profileType = kSRGB_SkColorProfileType;
+    }
 
     if (imageInfo) {
-        *imageInfo = SkImageInfo::Make(origWidth, origHeight, colorType, alphaType);
+        *imageInfo = SkImageInfo::Make(origWidth, origHeight, colorType, alphaType, profileType);

[scroggo, 2016/02/04 16:37:52]

conversion_possible checks to make sure the profile types match. So if someone
requests something like:

codec->getInfo().make<...>(...)

this will work, but if they call some versions of SkImageInfo::Make (without
selecting the right profile type), getPixels will fail.

This may be correct (?), but we should make sure that our existing tests use the
former and not the latter so we don't suddenly start failing. (Our tests should
catch us, though, I think.)

[msarett, 2016/02/04 16:44:35]

You're right.  This would break us all over the place (including in Android).
I would suggest that we change the check in conversion_possible to:
*** Always support linear (since right now we blindly output linear color
regardless of the encoded image)
*** Support sRGB if the encoded image is sRGB

What do you think?

[scroggo, 2016/02/04 16:53:01]

I think that's a fine choice for now. I think we have three choices for what to
do when linear is requested from an sRGB image:
- do a conversion to linear
- disallow linear
- silently give the sRGB version (this choice)

I don't know which one is correct, but maybe we should file a bug or a TODO to
fix to the right one?

[msarett, 2016/02/04 17:09:53]

sgtm

     }
     autoClean.detach();
     if (png_ptrp) {