Add three new histogram to tracking QUIC packet reordering:

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 357e28c2ca987420d18ed4cb081f574bcdd0bb0c..2c4056e9b2e422f2a7910d31216affae2e7250c9 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -13546,6 +13546,26 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Net.QuicSession.MaxReordering">
+  <owner>rch@chromium.org</owner>
+  <summary>The maximum reordering observed by a QUIC connection.</summary>

[Ian Swett, 2014/05/23 15:56:23]

Nit: comment that it's in sequence number space?

[Ryan Hamilton, 2014/05/23 16:19:15]

Done.

+</histogram>
+
+<histogram name="Net.QuicSession.MaxReorderingTime" units="percent">
+  <owner>rch@chromium.org</owner>
+  <summary>
+    The ratio of the maximum reordering time of a QUIC packet to the min rtt.
+  </summary>
+</histogram>
+
+<histogram name="Net.QuicSession.MaxReorderingTimeLongRtt" units="percent">
+  <owner>rch@chromium.org</owner>
+  <summary>
+    The ratio of the maximum reordering time of a QUIC packet to the min rtt,
+    only for those sessions with a min rtt larger than 100 ms.
+  </summary>
+</histogram>
+
 <histogram name="Net.QuicSession.NumOpenStreams">
   <owner>rch@chromium.org</owner>
   <summary>