Motivation: while experimenting with serializing images immediately, I would like to keep serializing metadata first. TBR=djsollen@google.com GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1780463008 Review URL: https://codereview.chromium.org/1780463008
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1689683002 Review URL: https://codereview.chromium.org/1689683002
Motivation: I want too finalize this API before working on the more complex problem of adding XMP metadata for PDF/A. BUG=skia:3110 Review URL: https://codereview.chromium.org/1359943003