If AspectRatioFitter is used with envelope parent mode then layouting is exhibiting a one frame delay when the game object containing the component is enabled

To reproduce:

1. Download attached project "AspectRatioFitterBug.zip" and open in Unity
2. Open "SampleScene" Scene
3. Enter Play mode
4. Click one of the buttons enabling a GameObject containing AspectRatioFitter
5. Observer how it takes one frame for it to do layouting

Notes:
- This issue reproduces on both Windows and OSX
- This issue reproduces on Standalone
- This bug seems to be the same as reported here:
https://issuetracker.unity3d.com/issues/the-aspectratiofitter-with-envelope-parent-mode-doesnt-control-the-recttransform-at-the-first-frame-after-changing-the-scene
- The difference is that in the reported issue the delay was after changing the scene, here it's just enabling a GameObject

Reproduced on Unity 2017.3.0f1, 2017.3.2f1, 2017.4.7f1, 2018.1.9f1, 2018.2.0f2 and 2018.3.0a5
Not reproduced on Unity 2017.2.3p2 and 2017.3.0b11
Regression on Unity 2017.3.0f1