how to solve Execution failed for task ':app:compileFlutterBuildDebug'
Something that work for me is: Delete your pubspec.lock, and get packages in your pubspec.yaml.
Try the following:
Go to pubspec.yaml file, and try doing Packages get | Pub get, and then build the project again.
Even if this doesn't work, try removing the import dart:html; from the code and build again.Hope this resolves!
Optimizing imports (Ctrl + Alt + O) in Android Studio solved the issue for me.