Felt crash on startup if full Dart SDK not built #65500
Description
If the engine wasn't built with --full-dart-sdk the felt tool crashes with a ProcessException when it tries to run dart2js. Looks like we check for the presence of pub but not dart2js (or other web tooling that guarantees we've built with --full-dart-sdk.
Example crash:
% ./lib/web_ui/dev/felt test
Running on MacOS. Will check the file and user limits.
File limits too low increasing the file limits
[Snapshot mode: on] (creating a new snapshot)
Running `pub get` in 'engine/src/flutter/lib/web_ui'
Resolving dependencies...
Got dependencies!
Running `pub get` in 'engine/src/flutter/web_sdk/web_engine_tester'
Resolving dependencies...
Got dependencies!
Building /Users/cbracken/src/flutter/engine/src/flutter/web_sdk/web_engine_tester/lib/static/host.dart.
Unhandled exception:
ProcessException: No such file or directory
Command: /Users/cbracken/src/flutter/engine/src/out/host_debug_unopt/dart-sdk/bin/dart2js lib/static/host.dart -o lib/static/host.dart.js