Reproduction Steps:
1. Open new Unity project
2. Select "Main Camera" in Hierarchy
3. Select "Background" color field in Inspector
4. Select Color Picker Tool
5. Move mouse outside the Unity Window on Chrome window
6. If it does not freeze
7. Press on Chrome window and make it active
8. Come back to Unity Window
9. Select Color Picker Tool
10. Move mouse outside the Unity Window on Chrome window
11. Notice that color picker Zoom Pixel Area is frozen

Expected Behaviour: Zoomed Pixel Area displays pixels that are currently under the cursor in real time.
Actual Result: Zoomed Pixel Area freezes if picker goes over Chrome window when it was last active (before Unity).

Reproduced on macOS
Reproduced on versions: Unity 5.5.4f1, 5.6.1p4, 2017.1.0b9, 2017.2.0a4