Treat IPv4-mapped IPv6 addresses as IPv4 addresses.

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
===================================================================
--- tools/metrics/histograms/histograms.xml	(revision 271511)
+++ tools/metrics/histograms/histograms.xml	(working copy)
@@ -13548,11 +13548,24 @@
 
 <histogram name="Net.QuicSession.PublicResetAddressMismatch"
     enum="QuicAddressMismatch">
-  <owner>rch@chromium.org</owner>
+  <owner>wtc@chromium.org</owner>
   <summary>
     When a public reset packet is received, whether the client IP address and
     port number in it differ from the client IP address and port number in the
     ServerHello handshake message. In the comparison, the first address is the
+    one in ServerHello and the second address is the one in public reset. Note:
+    this histogram is obsolete because it failed to treat IPv4-mapped IPv6
+    addresses as IPv4 addresses.
+  </summary>
+</histogram>
+
+<histogram name="Net.QuicSession.PublicResetAddressMismatch2"
+    enum="QuicAddressMismatch">
+  <owner>wtc@chromium.org</owner>
+  <summary>
+    When a public reset packet is received, whether the client IP address and
+    port number in it differ from the client IP address and port number in the
+    ServerHello handshake message. In the comparison, the first address is the
     one in ServerHello and the second address is the one in public reset.
   </summary>
 </histogram>