*: revendor dependencies after moving to go1.12

vendor/golang.org/x/net/trace/trace.go

@@ -64,6 +64,7 @@ package trace // import "golang.org/x/net/trace"
 
 import (
 	"bytes"
+	"context"
 	"fmt"
 	"html/template"
 	"io"
@@ -124,6 +125,18 @@ func init() {
 	http.HandleFunc("/debug/events", Events)
 }
 
+// NewContext returns a copy of the parent context
+// and associates it with a Trace.
+func NewContext(ctx context.Context, tr Trace) context.Context {
+	return context.WithValue(ctx, contextKey, tr)
+}
+
+// FromContext returns the Trace bound to the context, if any.
+func FromContext(ctx context.Context) (tr Trace, ok bool) {
+	tr, ok = ctx.Value(contextKey).(Trace)
+	return
+}
+
 // Traces responds with traces from the program.
 // The package initialization registers it in http.DefaultServeMux
 // at /debug/requests.