Introduce a trace wrapper

This patch introduces a wrapper to golang.org/x/net/trace with a new method
that will be useful later on, making logging and tracing less verbose.

internal/trace/trace.go

@@ -0,0 +1,44 @@
+// Package trace extends golang.org/x/net/trace.
+package trace
+
+import (
+	"fmt"
+
+	"github.com/golang/glog"
+	nettrace "golang.org/x/net/trace"
+)
+
+type Trace struct {
+	family string
+	title  string
+	t      nettrace.Trace
+}
+
+func New(family, title string) *Trace {
+	return &Trace{family, title, nettrace.New(family, title)}
+}
+
+func (t *Trace) LazyPrintf(format string, a ...interface{}) {
+	t.t.LazyPrintf(format, a...)
+
+	if glog.V(2) {
+		msg := fmt.Sprintf("%p %s %s: %+q", t, t.family, t.title,
+			fmt.Sprintf(format, a...))
+		glog.InfoDepth(1, msg)
+	}
+}
+
+func (t *Trace) SetError() {
+	t.t.SetError()
+}
+
+func (t *Trace) Errorf(format string, a ...interface{}) error {
+	err := fmt.Errorf(format, a...)
+	t.t.SetError()
+	t.LazyPrintf("Error: %v", err)
+	return err
+}
+
+func (t *Trace) Finish() {
+	t.t.Finish()
+}