Dart API changes:
* Loading units are a list and is an object now.
* Instance constants have a reference to their class definition.
JSON changes:
* loading units are a pool now.
* loading units are objects rather than only a string now.
* definitions are a pool now (so that const instances can refer to
them).
TEST=pkg/compiler/test/record_use/record_use_test.dart
TEST=pkg/dart2wasm/test/record_use_test.dart
TEST=pkg/vm/test/transformations/record_use_test.dart
Change-Id: I5fed1796d9cb08d6f0ade862ba2b4c3b5fea4ebd
Cq-Include-Trybots: luci.dart.try:dart2wasm-asserts-linux-chrome-try,dart2wasm-asserts-minified-linux-d8-try,dart2wasm-linux-chrome-try,dart2wasm-linux-d8-try,dart2wasm-linux-firefox-try,dart2wasm-linux-jscm-chrome-try,dart2wasm-linux-optimized-jsc-try,pkg-linux-debug-try,pkg-linux-release-arm64-try,pkg-linux-release-try,pkg-mac-release-arm64-try,pkg-mac-release-try,pkg-win-release-arm64-try,pkg-win-release-try,dart2js-canary-linux-try,dart2js-hostasserts-linux-d8-try,dart2js-linux-chrome-try,dart2js-linux-firefox-try,dart2js-mac-chrome-try,dart2js-mac-safari-try,dart2js-minified-csp-linux-chrome-try,dart2js-minified-linux-d8-try,dart2js-unit-linux-x64-release-try,dart2js-win-chrome-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/481860
Reviewed-by: Nate Biggs <natebiggs@google.com>
Commit-Queue: Daco Harkes <dacoharkes@google.com>
Daco Harkes
c24d130767