Show 2D Edge Collider as Gizmo, also in Edit Mode

showedgecollider.cs

using UnityEngine;
using System.Collections;

[ExecuteInEditMode]
public class visibleCollider : MonoBehaviour {

	// The Collider itself
	private EdgeCollider2D thisCollider;
	// array of collider points
	private Vector2[] points;
	// the transform position of the collider
	private Vector3 _t;

	void Start () {
		thisCollider = GetComponent ("EdgeCollider2D") as EdgeCollider2D;
		points = thisCollider.points;
		_t = thisCollider.transform.position;
	}

	void OnDrawGizmos() {
		Gizmos.color = Color.blue;
		// for every point (except for the last one), draw line to the next point
		for(int i = 0; i < points.Length-1; i++)
		{
			Gizmos.DrawLine(new Vector3(points[i].x+_t.x, points[i].y+_t.y), new Vector3(points[i+1].x+_t.x, points[i+1].y+_t.y));
		}
	}

}

Here is show 2d Polygon Collider https://gist.github.com/allfake/e899878b14cadf1e09d5.

add the "offset", then it's perfect ;)