wait until run button is pressed to run code (#1529)
wait until run button is pressed to run code (#1529)

* wait until run button is pressed to run code

Users could get stuck and be unable to fix snippets with infinite loops

* Run _performAnalysis on first load

* remove unused method
dart-lang/dart-pad,dart-lang/dart-pad,dart-lang/dart-pad,dart-lang/dart-pad