"Cannot measure duration of saving a Prefab. OnPrefabSavingStarted() has not been called first." error is thrown in the console on creating prefab after editing tile palette and not saving tile palette.

Steps to repro:
1. Hierarchy > 2D - Tilemap.
2. Window > Tile Palette.
3. Tile Palette > Create new Palette.
4. Drag any sprite and Paint a few tiles onto the tilemap.
5. Create any game object and drag into Assets to create a prefab.

Actual Result:
"Cannot measure duration of saving a Prefab. OnPrefabSavingStarted() has not been called first." error is thrown.

Expected Result:
Prefab should be created gracefully.

Occurs on:
2019.1.0a9, 2018.3.0b11, 2018.3.0a6

Working Fine on:
2018.3.0a5

NOTE: Improved Prefab has been introduced in 2018.3.0a6.

Environment:
Windows10, Windows 7 and Mac 10.13.