Steps to reproduce:
1. Have two monitors set up.
2. Open attached project (or create and open a new one).
3. Extend the width of "Editor" window, so that it would be visible in both screens.
4. Close the project.
5. Open the same project again.

Actual result:
The width of the "Editor" window is being adjusted to fit only the one screen.

Expected result:
When using two monitors and restarting Unity, the "Editor" window should remember its size and size should not be adjusted to fit only one screen automatically.

Reproduced with:
5.3.1f1, 5.3.4f1, 5.3.4p6, 5.4.0b18.

Cannot reproduce with:
5.1.0f3, 5.2.4f1.