Excluding Chrome's session storage from Time Machine
Since you're concerned about this occupying space unnecessarily, you could the exclude the folder. While you're at it, you could exclude the following folders since the rest (apart from Session Storage) are not useful to backup repeatedly/regularly either:


  ~/Library/Application Support/Google/Chrome/Default/Session Storage
  ~/Library/Application Support/Google/Chrome/Default/Local Storage
  ~/Library/Application Support/Google/Chrome/Default/Application Cache


In more recent versions of Chrome/OS X, these folders may be located in:

/Users/$USER/Library/Caches/Google/

Note that excluding Session Storage will prevent your sessions from being backed up - so you cannot restore back to older sessions from a backup.
Excluding Local Storage will prevent restoring the storage used by some/many web sites that use local storage to store information (to support offline use or for longer term identification).