Unity3D custom editor framing bounds

CustomComponent.cs

using UnityEngine;

class CustomComponent : MonoBehaviour
{
  // Configure custom world-space bounds as you like in the editor
  public Bounds CustomFocusBounds;
}

CustomComponentEditor.cs

using UnityEngine;
using UnityEditor;

[CustomEditor(typeof(CustomComponent))]
class CustomComponentEditor : EditorWindow
{
  // Called by SceneView to check if any of the components has custom frame bounds
  public bool HasFrameBounds()
  {
    return true;
  }

  // In case HasFrameBounds() returns true, this returns the custom world-space bounds used for framing
  public Bounds OnGetFrameBounds()
  {
    return (target as CustomComponent).CustomFocusBounds;
  }
}