anchor.diff:      stepIn.click(() => debuggerState.stepIn());
       stepOut.click(() => debuggerState.stepOut());
   
  -    final Map<String, dynamic> options = <String, dynamic>{
  -      'mode': 'dart',
  -      'lineNumbers': true,
  -      'gutters': <String>['breakpoints'],
  -    };
  -    final CodeMirror codeMirror =
  -        CodeMirror.fromElement(_sourceArea.element, options: options);
  -    codeMirror.setReadOnly(true);
  -    if (isDarkTheme) {
  -      codeMirror.setTheme('darcula');
  -    }
  -    final codeMirrorElement = _sourcePathDiv.element.parent.children[1];
  -    codeMirrorElement.setAttribute('flex', '');
  -
  -    sourceEditor = SourceEditor(codeMirror, debuggerState);
  -
  -    // TODO(#926): Is this necessary?
  -    sourceEditor.setBreakpoints(debuggerState.breakpoints.value);
  -    debuggerState.breakpoints.addListener(() {
  -      sourceEditor.setBreakpoints(debuggerState.breakpoints.value);
  -    });
  -
       void updateFrames() async {
         if (debuggerState.isPaused.value) {
           // Check for async causal frames; fall back to using regular sync frames.
  
positive.code:         callStackView.showFrames(frames, selectTop: true);
        } else {
          callStackView.clearFrames();
          sourceEditor.clearExecutionPoint();
        }
      }
  
  
negative.code:       sizes: [80, 20],
        minSize: [200, 60],
      );
  
      final options = <String, dynamic>{
        'mode': 'dart',
        'lineNumbers': true,
        'gutters': <String>['breakpoints'],
      };
      final codeMirror =
          CodeMirror.fromElement(_sourceArea.element, options: options);
      codeMirror.setReadOnly(true);
      if (isDarkTheme) {
        codeMirror.setTheme('darcula');
      }
      final codeMirrorElement = _sourcePathDiv.element.parent.children[1];
      codeMirrorElement.setAttribute('flex', '');
  
      sourceEditor = SourceEditor(codeMirror, debuggerState);
  
      // TODO(#926): Is this necessary?
      sourceEditor.setBreakpoints(debuggerState.breakpoints.value);
      debuggerState.breakpoints.addListener(() {
        sourceEditor.setBreakpoints(debuggerState.breakpoints.value);
      });
    }
  
    @override
  