Add browser_http_req_sending metric

This commit helps us move away from the k6 http_req_sending metric to
a browser prefixed one. It is custom to the browser module allowing the
user to measure k6 vs browser http_req_sending metrics separately.

common/network_manager.go

@@ -249,7 +249,7 @@ func (m *NetworkManager) emitResponseMetrics(resp *Response, req *Request) {
 					Time:       wallTime,
 				},
 				{
-					TimeSeries: k6metrics.TimeSeries{Metric: state.BuiltinMetrics.HTTPReqSending, Tags: tags},
+					TimeSeries: k6metrics.TimeSeries{Metric: m.customMetrics.BrowserHTTPReqSending, Tags: tags},
 					Value:      k6metrics.D(time.Duration(resp.timing.SendEnd-resp.timing.SendStart) * time.Millisecond),
 					Time:       wallTime,
 				},

k6ext/metrics.go

@@ -27,6 +27,7 @@ const (
 	browserHTTPReqDurationName       = "browser_http_req_duration"
 	browserHTTPReqConnectingName     = "browser_http_req_connecting"
 	browserHTTPReqTLSHandshakingName = "browser_http_req_tls_handshaking"
+	browserHTTPReqSendingName        = "browser_http_req_sending"
 )
 
 // CustomMetrics are the custom k6 metrics used by xk6-browser.
@@ -39,6 +40,7 @@ type CustomMetrics struct {
 	BrowserHTTPReqDuration       *k6metrics.Metric
 	BrowserHTTPReqConnecting     *k6metrics.Metric
 	BrowserHTTPReqTLSHandshaking *k6metrics.Metric
+	BrowserHTTPReqSending        *k6metrics.Metric
 }
 
 // RegisterCustomMetrics creates and registers our custom metrics with the k6
@@ -80,6 +82,7 @@ func RegisterCustomMetrics(registry *k6metrics.Registry) *CustomMetrics {
 		BrowserHTTPReqDuration:       registry.MustNewMetric(browserHTTPReqDurationName, k6metrics.Trend, k6metrics.Time),
 		BrowserHTTPReqConnecting:     registry.MustNewMetric(browserHTTPReqConnectingName, k6metrics.Trend, k6metrics.Time),
 		BrowserHTTPReqTLSHandshaking: registry.MustNewMetric(browserHTTPReqTLSHandshakingName, k6metrics.Trend, k6metrics.Time),
+		BrowserHTTPReqSending:        registry.MustNewMetric(browserHTTPReqSendingName, k6metrics.Trend, k6metrics.Time),
 	}
 }