Add count to TouchEventReported atom

We might have to reconstruct mean and st. dev. over arbitrary periods of
time and across multiple devices. Currently, we are just looking at the
average and st. dev. values. In order to be able to reconstruct, we need
to know the number of events in each chunk that is received.

Add the needed field here.

Bug: 111431676
Test: out/host/linux-x86/bin/statsd_testdrive 34
Change-Id: I5aa4b759404308b98d4e6b5ed5a94e4c760dc447

cmds/statsd/src/atoms.proto

@@ -2431,6 +2431,8 @@ message TouchEventReported {
     optional float latency_mean_micros = 3;
     // Standard deviation
     optional float latency_stdev_micros = 4;
+    // Number of touch events (input_event) in this report
+    optional int32 count = 5;
 }
 
 /**