KeyboardEvents are only rounding to 100ms

In legacy/trac#1517 (moved), the idea was to round most event time stamps to 100ms, but to round KeyboardEvent.timeStamp to 250 ms (see https://trac.torproject.org/projects/tor/ticket/1517#comment:25).

Our current patch for legacy/trac#1517 (moved) is here.

However, when I test KeyboardEvents in the latest Tor Browser, I only see rounding to 100 ms. With the debugger I observed that calling myKeyboardEvent.timeStamp in the browser console is calling Event::TimeStamp() instead of KeyboardEvent::TimeStamp. So we're apparently failing to properly override the Event::TimeStamp call.