NQE: Record the number of RTT and throughput samples received

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index ba8d793e5e21aba7cef14116a85590721f466646..b7ae436341e16d8a68749bd8990ce128a1f38658 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -41157,6 +41157,16 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="NQE.Kbps.ObservationSource" enum="NQEObservationSource">
+  <owner>tbansal@chromium.org</owner>
+  <owner>bengr@chromium.org</owner>
+  <summary>
+    Number of Kbps observations indexed by the source of the observation.
+    Recorded by the network quality estimator every time a new observation is
+    made or synthesized.
+  </summary>
+</histogram>
+
 <histogram name="NQE.Kbps.OnECTComputation" units="Kbps">
   <owner>bengr@chromium.org</owner>
   <owner>tbansal@chromium.org</owner>
@@ -41287,6 +41297,16 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="NQE.RTT.ObservationSource" enum="NQEObservationSource">
+  <owner>tbansal@chromium.org</owner>
+  <owner>bengr@chromium.org</owner>
+  <summary>
+    Number of RTT observations indexed by the source of the observation.
+    Recorded by the network quality estimator every time a new observation is
+    made or synthesized.
+  </summary>
+</histogram>
+
 <histogram name="NQE.RTT.OnECTComputation" units="ms">
   <owner>bengr@chromium.org</owner>
   <owner>tbansal@chromium.org</owner>
@@ -99930,6 +99950,17 @@ value.
              provider"/>
 </enum>
 
+<enum name="NQEObservationSource" type="int">
+  <int value="0" label="HTTP"/>
+  <int value="1" label="TCP"/>
+  <int value="2" label="QUIC"/>
+  <int value="3" label="HTTP-layer cached"/>
+  <int value="4" label="HTTP-layer default"/>
+  <int value="5" label="HTTP-layer external estimate provider"/>
+  <int value="6" label="Transport-layer cached"/>
+  <int value="7" label="Transport-layer default"/>
+</enum>
+
 <enum name="NtpFollowAction" type="int">
   <int value="0" label="PAGE_TRANSITION_LINK"/>
   <int value="1" label="PAGE_TRANSITION_TYPED"/>