Rename time to event in Soong metrics system.

Several structs and files are named time which records the total
execution of a traceable event. Soon, resource information of an
executed process is collected during a build event so a more generic
name is applied.

Bug: b/169453825
Test: go test and m nothing. Checked the soong_metrics protobuf.
Change-Id: I65a782603530d51018d6cc1192c18cfeef7566a0
diff --git a/ui/build/context.go b/ui/build/context.go
index 3945ce0..43e1e0f 100644
--- a/ui/build/context.go
+++ b/ui/build/context.go
@@ -48,7 +48,7 @@
 		c.Tracer.Begin(desc, c.Thread)
 	}
 	if c.Metrics != nil {
-		c.Metrics.TimeTracer.Begin(name, desc, c.Thread)
+		c.Metrics.EventTracer.Begin(name, desc, c.Thread)
 	}
 }
 
@@ -58,7 +58,7 @@
 		c.Tracer.End(c.Thread)
 	}
 	if c.Metrics != nil {
-		c.Metrics.SetTimeMetrics(c.Metrics.TimeTracer.End(c.Thread))
+		c.Metrics.SetTimeMetrics(c.Metrics.EventTracer.End(c.Thread))
 	}
 }