Instrumentation: Add examplars for request histograms (#29357)

Signed-off-by: bergquist <carl.bergquist@gmail.com>

pkg/middleware/logger.go

@@ -16,15 +16,13 @@
 package middleware
 
 import (
-	"context"
 	"net/http"
 	"time"
 
 	"github.com/grafana/grafana/pkg/models"
 	"github.com/grafana/grafana/pkg/setting"
-	opentracing "github.com/opentracing/opentracing-go"
 	"github.com/prometheus/client_golang/prometheus"
-	"github.com/uber/jaeger-client-go"
+	cw "github.com/weaveworks/common/middleware"
 	"gopkg.in/macaron.v1"
 )
 
@@ -63,7 +61,7 @@ func Logger() macaron.Handler {
 				"referer", req.Referer(),
 			}
 
-			traceID, exist := extractTraceID(ctxTyped.Req.Request.Context())
+			traceID, exist := cw.ExtractTraceID(ctxTyped.Req.Request.Context())
 			if exist {
 				logParams = append(logParams, "traceID", traceID)
 			}
@@ -76,16 +74,3 @@ func Logger() macaron.Handler {
 		}
 	}
 }
-
-func extractTraceID(ctx context.Context) (string, bool) {
-	sp := opentracing.SpanFromContext(ctx)
-	if sp == nil {
-		return "", false
-	}
-	sctx, ok := sp.Context().(jaeger.SpanContext)
-	if !ok {
-		return "", false
-	}
-
-	return sctx.TraceID().String(), true
-}