GetEditorMainWindowPos

private static bool         initializedMainViewMetadata;
private static Type         containerWinType;
private static FieldInfo    showModeField;
private static PropertyInfo positionProperty;

private static object   mainWindow;

public static Rect  GetEditorMainWindowPos()
{
    if (Utility.initializedMainViewMetadata == false)
    {
        Utility.initializedMainViewMetadata = true;
        Utility.LazyInitializeMainViewMetadata();
    }

    if (Utility.containerWinType == null)
        return default(Rect);

    if (Utility.mainWindow == null || Utility.mainWindow.Equals(null) == true || Object.Equals(Utility.mainWindow, "null") == true)
    {
        Object[]    windows = Resources.FindObjectsOfTypeAll(containerWinType);
        foreach (Object win in windows)
        {
            int showmode = (int)Utility.showModeField.GetValue(win);
            if (showmode == 4) // main window
            {
                Utility.mainWindow = win;
                break;
            }
        }
    }

    if (Utility.mainWindow.Equals(null) == false)
        return (Rect)Utility.positionProperty.GetValue(Utility.mainWindow, null);

    throw new NotSupportedException("Can't find internal main window. Maybe something has changed inside Unity.");
}

[AssemblyVerifier]
private static void LazyInitializeMainViewMetadata()
{
    Utility.containerWinType = AssemblyVerifier.TryGetType(typeof(Editor).Assembly, "UnityEditor.ContainerWindow");
    if (Utility.containerWinType != null)
    {
        Utility.showModeField = AssemblyVerifier.TryGetField(Utility.containerWinType, "m_ShowMode", BindingFlags.NonPublic | BindingFlags.Instance);
        Utility.positionProperty = AssemblyVerifier.TryGetProperty(Utility.containerWinType, "position", BindingFlags.Public | BindingFlags.Instance);

        if (Utility.showModeField == null || Utility.positionProperty == null)
            Utility.containerWinType = null;
    }
}