We called JsonWriter::DumpJson() every once in a while,
but this did not necssarily wait for offloaded PNG encoding to finish.
This means we might have been dropping some DM results for a while now.
Fix by one more JsonWriter::DumpJson() call after joining back to the
main thread.
BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=
1744723002
Review URL: https://codereview.chromium.org/
1744723002
// We'd better have run everything.
SkASSERT(gPending == 0);
+ // Make sure we've flushed all our results to disk.
+ JsonWriter::DumpJson();
// At this point we're back in single-threaded land.
sk_tool_utils::release_portable_typefaces();