From lldb:

"""
(lldb) bt
* thread #38: tid = 0x563be, 0x00007fffe5bef318 UserActivity`-[UAUserActivity encodeUserInfo:error:], queue = 'com.apple.root.default-qos', stop reason = breakpoint 1.1
  * frame #0: 0x00007fffe5bef318 UserActivity`-[UAUserActivity encodeUserInfo:error:]
    frame #1: 0x00007fffe5bf62fa UserActivity`-[UAUserActivity(Internal) userActivityInfoForSelf] + 2159
    frame #2: 0x00007fffe5bf6e0c UserActivity`-[UAUserActivity(Internal) callWillSaveDelegateIfDirtyAndPackageUpData:clearDirty:] + 2636
    frame #3: 0x00007fffe5bf7dea UserActivity`-[UAUserActivity(Internal) sendUserActivityInfoToLSUserActivityd:onAsyncQueue:] + 1762
    frame #4: 0x00007fffe847af57 libdispatch.dylib`_dispatch_call_block_and_release + 12
    frame #5: 0x00007fffe8472120 libdispatch.dylib`_dispatch_client_callout + 8
    frame #6: 0x00007fffe84812c6 libdispatch.dylib`_dispatch_queue_override_invoke + 743
    frame #7: 0x00007fffe8473ed8 libdispatch.dylib`_dispatch_root_queue_drain + 476
    frame #8: 0x00007fffe8473caf libdispatch.dylib`_dispatch_worker_thread3 + 99
    frame #9: 0x00007fffe86be756 libsystem_pthread.dylib`_pthread_wqthread + 1299
    frame #10: 0x00007fffe86be231 libsystem_pthread.dylib`start_wqthread + 13
"""
I suspect this message gets sent each time Chrome update the url to send to handoff. I didn't see any easy way of suppressing this message.