A helper class for drawing a transform's rotation field in the same way as the Transform editor in Unity.

Transform Rotation GUI

using System;
using System.Reflection;
using UnityEngine;
using UnityEditor;

/// <summary>
/// Abstracts the reflection required to use the internal TransformRotationGUI class.
/// </summary>
public class TransformRotationGUI
{
	private object transformRotationGUI;
	private MethodInfo onEnable;
	private MethodInfo rotationField;

	public TransformRotationGUI ()
	{
		if (transformRotationGUI == null)
		{
			var type = Type.GetType ("UnityEditor.TransformRotationGUI,UnityEditor");

			onEnable = type.GetMethod ("OnEnable");
			rotationField = type.GetMethod ("RotationField", new Type[] { });

			transformRotationGUI = Activator.CreateInstance (type);
		}
	}

	/// <summary>
	/// Initializes the GUI.
	/// </summary>
	public void Initialize (SerializedProperty property, GUIContent content)
	{
		onEnable.Invoke (transformRotationGUI, new object[] { property, content });
	}

	/// <summary>
	/// Draws the rotation GUI.
	/// </summary>
	public void Draw ()
	{
		rotationField.Invoke (transformRotationGUI, null);
	}
}