Delete code to fallback to the dart:html version of the app. (#2713)

Leave the index_fallback.html as an escape hatch to debug if users hit issues or IDEs need to fallback.

packages/devtools_app/lib/main.dart

@@ -9,50 +9,10 @@ import 'src/analytics/stub_provider.dart'
 import 'src/app.dart';
 import 'src/config_specific/framework_initialize/framework_initialize.dart';
 import 'src/config_specific/ide_theme/ide_theme.dart';
-import 'src/config_specific/load_fallback_app/load_fallback_app.dart';
 import 'src/debugger/syntax_highlighter.dart';
 import 'src/preferences.dart';
 
 void main() async {
-  final defaultOnError = FlutterError.onError;
-  var numErrors = 0;
-  var fallbackVersionDialogShown = false;
-
-  // The SKIA/CanvasKit version of Flutter Web is newer than other platforms
-  // and depends on WebGL so we need to detect whether it is behaving badly
-  // to give users the option to reopen DevTools using a fallback slower version
-  // that may be more stable.
-  // TODO(jacobr): remove this error listening code once
-  // https://github.com/flutter/devtools/issues/2125 is fixed.
-  if (const bool.fromEnvironment('FLUTTER_WEB_USE_SKIA')) {
-    FlutterError.onError = (FlutterErrorDetails details) {
-      if (defaultOnError != null) {
-        defaultOnError(details);
-      }
-      final bool overflowError = details.toString().contains('overflowed');
-
-      if (overflowError) {
-        // Overflow errors do not indicate a CanvasKit specific problem and
-        // occur frequently in debug builds of apps so we filter them out to
-        // avoid distraction. We could alternately suppress this code completely
-        // in debug builds but it is risky to add code that runs in release
-        // builds but not debug builds.
-        return;
-      }
-      // TODO(jacobr): detect SKIA specific errors and warn on the first SKIA
-      // specific error rather than waiting for multiple errors.
-      numErrors++;
-      if (numErrors >= 20 && !fallbackVersionDialogShown) {
-        fallbackVersionDialogShown = true;
-        promptToLoadFallbackApp(
-          "The Flutter web backend ('CanvasKit') has encountered multiple errors.\n"
-          'Would you like to open a fallback version of DevTools that is '
-          'slower but does not depend on WebGL?',
-        );
-      }
-    };
-  }
-
   final ideTheme = getIdeTheme();
 
   final preferences = PreferencesController();