This class allows a client of SkCodec to read chunks in the data
stream that are not recognized by libpng. This is used by Android
to specify ninepatch data.
Taken from SkImageDecoder::Peeker. Modify the name of the class
and its method to be more specific to their use. Make
SkImageDecoder::Peeker a subclass of the new class, to help stage
the change in Android.
Add a test to verify that it works.
BUG=skia:4574
BUG=skia:3257
Committed: https://skia.googlesource.com/skia/+/3389e00136188800b98ca69488c0418c374fd78b
Review URL: https://codereview.chromium.org/1040453002
cf98fa9311