Does the chrome browser behave differently when the computer is locked, or the window is not in the foreground? I am noticing that page load slower in such use cases on windows.
If so can this be disabled through any of their flags?
The simple answer is no. Google Chrome does not behave differently when the computer is locked or the browser is not full screen.
The slightly longer answer is that when the screen is locked, the user is still logged in, and all user applications continue to run as normal but on the user-desktop rather than the secure desktop. All drawing events are shortcircuited to avoid wasting CPU drawing frames that aren't going to be shown, but nothing much else happens that Google Chrome will see.
One other feature of running in the background is that threads get smaller timeslices when they are not in the foreground - a deliberate feature in Windows because a 5% slowdown on a foreground thread can make the system appear slow, whereas a 5% slowdown on a background process is usually unnoticeable.
In Windows this same principle also carries over for network and disk latency. Foreground threads are given priority for queued network operations, so if thirty threads all want to do DNS lookups (as may very well be the case if you open loads of new tabs in Chrome), the ones that happen first are the ones for the tab you're looking at.
A combination of all of these factors means that when Google Chrome isn't in the foreground (e.g. because something else is, or the machine is locked) and other things are going on in the system, Google Chrome may perform less well than if it were in the foreground.
Ultimately though, this is Windows being clever and trying to make your user-experience less sluggish, not Google Chrome doing anything different.
Yes, Chrome does set a much lower priority to background tabs.