Input latency

[Daniel van Vugt]

Here are some fun numbers I've collected about the latency between input 
events sent from the top-level Mir server to a client. All in 
milliseconds...

Desktop (3.12.0-7-generic)
Direct 0.8ms
Nested 1.3ms

Desktop (3.11.0-11-lowlatency)
Direct 1.0ms
Nested 1.7ms

Nexus4 (3.4.0-3-mako)
Direct 0.9ms
Nested 1.5ms with high variance; frequent spikes to 73ms. Sometimes 700ms.

The above numbers are for motion events. Key events appear to be twice 
as fast (half the latency). This suggests we could yet optimize the 
processing of motion events to perform better like key events do.

In summary, we're looking pretty good. Only the Nexus has potential 
usability issues, and even then, only with nested servers.

- Daniel