add opentracing spans for metrics

vendor/github.com/openzipkin/zipkin-go-opentracing/raw.go

@@ -0,0 +1,30 @@
+package zipkintracer
+
+import (
+	"time"
+
+	opentracing "github.com/opentracing/opentracing-go"
+)
+
+// RawSpan encapsulates all state associated with a (finished) Span.
+type RawSpan struct {
+	// Those recording the RawSpan should also record the contents of its
+	// SpanContext.
+	Context SpanContext
+
+	// The name of the "operation" this span is an instance of. (Called a "span
+	// name" in some implementations)
+	Operation string
+
+	// We store <start, duration> rather than <start, end> so that only
+	// one of the timestamps has global clock uncertainty issues.
+	Start    time.Time
+	Duration time.Duration
+
+	// Essentially an extension mechanism. Can be used for many purposes,
+	// not to be enumerated here.
+	Tags opentracing.Tags
+
+	// The span's "microlog".
+	Logs []opentracing.LogRecord
+}