The hot reload runner currently only supports d8, but I plan to add support for Chrome and VM execution.
Notable changes:
* Creates `package:reload_test` with helpers for running this suite.
* Updates the module loader with D8-specific branches and hooks for hot reload/restart.
* Exposes DDC runtime variables via a `HotReloadTestRuntime` API.
* Ports constant equality hot restart tests from webdev/dwds (validated to fail if either cache-clearing mechanism fails).
* Partially rolls DDC's d8 preamble forward (towards dart2js's).
* Wraps D8's timer implementation with custom timeout logic to better match Chrome's timing semantics when executing with native JS async.
Tests for the framework and matrix updates will be added in an upcoming change.
Change-Id: I2773b29f464cfd0330e4c653c05e117ae150b4a6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/350021
Reviewed-by: Sigmund Cherem <sigmund@google.com>
Reviewed-by: Nicholas Shahan <nshahan@google.com>
Commit-Queue: Mark Zhou <markzipan@google.com>
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