Gather histogram for received packets indicating losses.

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 f411637178c9dfc7034c2ba930c04f3f6ce247da..c5da07f1d2eaaf0ae46037966615ad1492f29e9b 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -10228,6 +10228,22 @@ other types of suffix sets.
   </summary>
 </histogram>
 
+<histogram name="Net.QuicSession.PacketReceived_Ack" units="SequenceNumber">
+  <summary>
+    Each bucket contains the number of packets with a corresponding sequence
+    number that were received by the client, and hence the client ACKed the
+    packet.
+  </summary>
+</histogram>
+
+<histogram name="Net.QuicSession.PacketReceived_Nack" units="SequenceNumber">
+  <summary>
+    Each bucket contains the number of packets with a corresponding sequence
+    number were not received by the client, but for which there were later
+    packet sequence numbers received, and hence the client NACKed the packet.
+  </summary>
+</histogram>
+
 <histogram name="Net.QuicSession.PublicResetAddressMismatch"
     enum="QuicAddressMismatch">
   <summary>
@@ -34513,6 +34529,23 @@ other types of suffix sets.
   <affected-histogram name="Media.VideoCaptureManager"/>
 </fieldtrial>
 
+<fieldtrial name="Net.QuicSession.PacketReceived" separator="_">
+  <group name="CONNECTION_UNKNOWN" label="Connections via WiFi are tallied."/>

[Ryan Hamilton, 2014/03/07 17:47:05]

nit: I'm not sure that "are tallied" adds any value here since the tallying is
pretty much what a histogram does.  Your call though.

[jar (doing other things), 2014/03/07 18:01:11]

This line of text is added to the "prose" section that provides a description of
the histogram.  As a result, I try to use full sentences here (unlike an enum,
which provides a super-terse description of a bucket).

As a result, I have to say something like:

This histogram only includes data about WiFi connections.

I was looking for a short sentence to convey that.... but I can go longer if you
have a better sentence in mind.

+  <group name="CONNECTION_ETHERNET"
+      label="Connections via ethernet are tallied, but this may include
+             connections to a wifi bridge."/>
+  <group name="CONNECTION_WIFI"
+      label="Connections via WiFi are tallied, but this may include
+             connections to a mobile hotspot."/>
+  <group name="CONNECTION_2G" label="Connections mobile 2G are tallied."/>

[Ryan Hamilton, 2014/03/07 17:47:05]

nit: did you mean to say "*via* mobile" here and below?

[jar (doing other things), 2014/03/07 18:01:11]

Done.

+  <group name="CONNECTION_3G" label="Connections mobile 3G are tallied."/>
+  <group name="CONNECTION_4G" label="Connections mobile 4G are tallied."/>
+  <group name="CONNECTION_NONE"
+      label="Connections via NO(?) network are tallied (should be empty)."/>
+  <affected-histogram name="Net.QuicSession.PacketReceived_Ack"/>
+  <affected-histogram name="Net.QuicSession.PacketReceived_Nack"/>
+</fieldtrial>
+
 <fieldtrial name="NetConnectivity" separator=".">
   <group name="53.100B" label="100 bytes of data on port 53."/>
   <group name="53.100B.NoProxy"