SetGameViewSize.cs

using UnityEngine;
using UnityEditor;
/*
 * orignially posted
 http://answers.unity3d.com/questions/179775/game-window-size-from-editor-window-in-editor-mode.html
 */

public class SetGameViewSize : EditorWindow {

    private Vector2 _size = new Vector2(800, 600);

    [MenuItem("Window/Set Window Size")]
    static void Init() {
        SetGameViewSize window = (SetGameViewSize)(EditorWindow.GetWindow(typeof(SetGameViewSize)));
    } // Init()

    public static EditorWindow GetMainGameView() {
        System.Type T = System.Type.GetType("UnityEditor.GameView,UnityEditor");
        System.Reflection.MethodInfo GetMainGameView = T.GetMethod("GetMainGameView", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Static);
        System.Object Res = GetMainGameView.Invoke(null, null);
        return (EditorWindow)Res;
    } // GetMainGameView()

    void OnGUI() {
        _size.x = EditorGUILayout.IntField("X", (int)_size.x);
        _size.y = EditorGUILayout.IntField("Y", (int)_size.y);
        if (GUILayout.Button("Set")) {
            Set();
        }
        if (GUILayout.Button("2048*1536")) {
            _size.Set(2048, 1536);
            Set();
        }    	
        if (GUILayout.Button("1024*768")) {
            _size.Set(1024, 768);
            Set();
        }
        if (GUILayout.Button("960*640")) {
            _size.Set(960, 640);
            Set();       
        }
        if (GUILayout.Button("800*480")) {
            _size.Set(800, 480);
            Set();
        }

    } // OnGUI()
    void Set() {
        EditorWindow gameView = GetMainGameView();
        Rect pos = gameView.position;
        pos.y = pos.y - 0;
        pos.width = _size.x;
        pos.height = _size.y + 17;
        gameView.position = pos;
    }
}