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/test_build.go b/ui/build/test_build.go
index 348d41f..5109465 100644
--- a/ui/build/test_build.go
+++ b/ui/build/test_build.go
@@ -22,6 +22,7 @@
 	"sort"
 	"strings"
 
+	"android/soong/ui/metrics"
 	"android/soong/ui/status"
 )
 
@@ -37,7 +38,7 @@
 		return
 	}
 
-	ctx.BeginTrace("test for dangling rules")
+	ctx.BeginTrace(metrics.TestRun, "test for dangling rules")
 	defer ctx.EndTrace()
 
 	ts := ctx.Status.StartTool()