Add a Ping() method to the trace service to make it easier to detect if the service is up and runni…

trace/service/traceservice_test.go

Index: trace/service/traceservice_test.go
diff --git a/trace/service/traceservice_test.go b/trace/service/traceservice_test.go
index 88954bed8b0c5100965fab938a934ffe0548a46d..09c12e146a8d6ac13c0e16a82465401ba505130e 100644
--- a/trace/service/traceservice_test.go
+++ b/trace/service/traceservice_test.go
@@ -108,6 +108,10 @@ func TestImpl(t *testing.T) {
 
 	ctx := context.Background()
 
+	// First confirm that Ping() works.
+	_, err = ts.Ping(ctx, &Empty{})
+	assert.Nil(t, err)
+
 	// Confirm that these traceids don't have Params stored in the db yet.
 	missingRequest := &MissingParamsRequest{
 		Traceids: []string{"key:8888:android", "key:gpu:win8"},