Unless you've explicitly
ulimited Chrome, the Linux kernel gives a process as much memory as it demands (up to the limit of virtual memory available). And Chromium will eat up gigabytes of memory if you have enough tabs open.
If you have a small amount of RAM (no more than a few gigabytes), you could add more, but realistically a single browser game shouldn't be eating up that much.
Otherwise, there's nothing you can do to allocate more memory to it, other than patching the Chromium codebase to use more memory :).
In short, I doubt lack of memory is the reason for choppiness (it's probably CPU-bound, or GPU-bound if the game uses WebGL). But fixing that is a different question.