We rename constant names to use lowerCamelCase, and append
"AttributeName" in most cases, as most constants refer to a (as it is
documented) "JSON attribute."
Additionally the `toJson` methods can be simplified by returning
Map literals, instead of setting key/value pairs in individual
statements.
Change-Id: I5f0adabfa3c4d274407ae8a5b5684dce22f9b5fa
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/455880
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Sam Rawlins
a2e9153029