Load Asset Bundle in Editor

I have actually accomplished this with my own script. You have the wrong idea here, you cannot use StartCoroutine except during runtime. My script is designed to not freeze up the editor while running. Use this instead:

 public class DecryptAssetBundle : EditorWindow {
 
 private string assetURL = "";
 private static WWW request;
 
 private static bool run = false;
 private static IEnumerator en = null;
 
 [MenuItem("Bundles/Decrypt Asset Bundle")]
 static void Init () {    
     DecryptAssetBundle window = EditorWindow.GetWindow(typeof(DecryptAssetBundle)) as DecryptAssetBundle;
     window.position = new Rect(Screen.width/2,Screen.height/2, 400,150);
 }
 void OnGUI()
 {
     assetURL = EditorGUILayout.TextField("Asset bundle URL: ", assetURL);
 
     GUILayout.BeginHorizontal();
     if(GUILayout.Button("Clear"))
     {
         assetURL = "";
     }
     if(GUILayout.Button("Decrypt"))
     {
         run=true;
     }
     if(GUILayout.Button("Abort"))
     {
         run=false;
     }
     GUILayout.EndHorizontal();
 }
 
 public void Update() {
     if (!run) {
         if (en != null)
             en = null;
         return;
     }
     if (en == null) {
         en = LoadAsset(assetUrl);
     }
     if (! en.MoveNext())
         run=false;
 }
 
 private IEnumerator LoadAsset(string s)
 {
     Debug.Log("Loading " + s + " ...");
     request = new WWW(s);
     while (! request.isDone)
         // avoid freezing the editor:
         yield return ""; // just wait.
     // I don't like the following line because it will freeze up 
     // your editor.  So I commented it out.  
     // yield return request;
     if(request.error != null)
         Debug.LogError(request.error);
     GameObject g = (GameObject) request.assetBundle.mainAsset as GameObject;
     Instantiate(g);
 }
 
 }