track flags in a map
track flags in a map

I got to thinking that seeing flags like,

    out/fm --nonativeFonts -b cpu --nativeFonts -s ...

is kind of confusing, and I'm also trying to figure out
how to identify these runs to Gold.  I think the answer
to both might be to track a map[string]string for flags,
allowing overrides rather than just appending, and then
that flag map ends up being the identifying properties.

Change-Id: Ie5f80ee8b145c205edc768ae871eb70a3e1bc5b7
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/378355
Reviewed-by: Eric Boren <0e499112533c8544f0505ea0d08394fb5ad7d8fa@google.com>

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