Add performance counter metrics to build.trace.gz

Start a background goroutine at the beginning of soong_build that
captures the CPU usage, heap size, and total system memory every
second.  Propagate the values through soong_build_metrics.pb back
to soong_ui, and then into build.trace.gz.

Test: m nothing, examine build.trace.gz
Change-Id: Iad99f8f1f088f4f7f7d5f76566a38c0c4f4d0daa

ui/build/soong.go

@@ -15,6 +15,7 @@
 package build
 
 import (
+	"android/soong/ui/tracer"
 	"fmt"
 	"io/fs"
 	"os"
@@ -774,6 +775,19 @@ func loadSoongBuildMetrics(ctx Context, config Config, oldTimestamp time.Time) {
 		ctx.Tracer.Complete(desc, ctx.Thread,
 			event.GetStartTime(), event.GetStartTime()+event.GetRealTime())
 	}
+	for _, event := range soongBuildMetrics.PerfCounters {
+		timestamp := event.GetTime()
+		for _, group := range event.Groups {
+			counters := make([]tracer.Counter, 0, len(group.Counters))
+			for _, counter := range group.Counters {
+				counters = append(counters, tracer.Counter{
+					Name:  counter.GetName(),
+					Value: counter.GetValue(),
+				})
+			}
+			ctx.Tracer.CountersAtTime(group.GetName(), ctx.Thread, timestamp, counters)
+		}
+	}
 }
 
 func runMicrofactory(ctx Context, config Config, name string, pkg string, mapping map[string]string) {