[SurfaceFlinger] Push atoms on janky events

For now define a jank event as a window of 100ms containing at least one
missed frame. On the server-side we can then configure whether tracing
is triggered based on the number of missed frames in a window.

A 100ms window should be safe, as always-on tracing should contain ~10
seconds of trace data

Further details on when we report a jank:
* We don't report a jank if it occurred more than a second in the past,
since we need a good guarantee that the trace will actually contain the
jank
* We don't report a jank if the display is off or in doze, as missed
frames in those power modes are either not actionable or not
user-perceived.
* We only report a jank on userdebug or eng builds. This will never be
enabled on user builds, so there's no reason to incur the cost of
pushing the atom on those builds.

Bug: 148543048
Test: builds
Test: statsd_testdrive 257
Change-Id: Ifc544d544ef8da9adec944507fe71dc5550c13e8