Generate build timing metrics to proto format file

Test: Dumped the text formated based metrics file to out dir,
and checked the file.
Bug: b/63815990

Change-Id: Iff476f72a0be74eb53b6b26ef468d11c0f24a404
diff --git a/ui/build/kati.go b/ui/build/kati.go
index d2e9fe9..205d5ae 100644
--- a/ui/build/kati.go
+++ b/ui/build/kati.go
@@ -21,6 +21,7 @@
 	"path/filepath"
 	"strings"
 
+	"android/soong/ui/metrics"
 	"android/soong/ui/status"
 )
 
@@ -101,7 +102,7 @@
 }
 
 func runKatiBuild(ctx Context, config Config) {
-	ctx.BeginTrace("kati build")
+	ctx.BeginTrace(metrics.RunKati, "kati build")
 	defer ctx.EndTrace()
 
 	args := []string{
@@ -137,7 +138,7 @@
 }
 
 func runKatiPackage(ctx Context, config Config) {
-	ctx.BeginTrace("kati package")
+	ctx.BeginTrace(metrics.RunKati, "kati package")
 	defer ctx.EndTrace()
 
 	args := []string{
@@ -178,7 +179,7 @@
 }
 
 func runKatiCleanSpec(ctx Context, config Config) {
-	ctx.BeginTrace("kati cleanspec")
+	ctx.BeginTrace(metrics.RunKati, "kati cleanspec")
 	defer ctx.EndTrace()
 
 	runKati(ctx, config, katiCleanspecSuffix, []string{