Replace SSLProtocolNegotiation histogram with SSLNegotiatedAlpnProtocol.

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 0f5c2c4e54dc52d5c3d392adc9f14d1ffd369e84..ac091c8e40ee62dc21032a38cc4fa0f059069857 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -26500,6 +26500,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Net.AlpnNegotiatedProtocol" enum="AlpnNegotiatedProtocol">
+  <owner>bnc@chromium.org</owner>
+  <summary>
+    Whether the server included an ALPN extension in the TLS server hello; and
+    if so, the negotiated protocol.

[davidben, 2016/08/17 19:44:11]

For each TLS handshake, whether ALPN was negotiated and, if so, the negotiated
protocol.

(The message is called ServerHello, but it's not even going to be in the
ServerHello in TLS 1.3. Better to speak in terms of high-level things.)

[Bence, 2016/08/18 13:37:34]

Done.

+  </summary>
+</histogram>
+
 <histogram name="Net.AlternateProtocolBrokenLocation"
     enum="BrokenAlternateProtocolLocation">
   <owner>rch@chromium.org</owner>
@@ -31911,6 +31919,9 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 </histogram>
 
 <histogram name="Net.SSLProtocolNegotiation" enum="SSLProtocolNegotiation">
+  <obsolete>
+    Superseded by Net.AlpnNegotiatedProtocol in 2016 August.
+  </obsolete>
   <owner>bnc@chromium.org</owner>
   <summary>
     TLS extension used to negotiate protocol (ALPN or NPN); in case of NPN,
@@ -67034,6 +67045,12 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="2" label="Malformed response"/>
 </enum>
 
+<enum name="AlpnNegotiatedProtocol" type="int">
+  <int value="0" label="ALPN not used"/>
+  <int value="1" label="HTTP/1.1 negotiated via ALPN"/>
+  <int value="2" label="HTTP/2 negotiated via ALPN"/>
+</enum>
+
 <enum name="AlternateProtocolUsage" type="int">
   <int value="0" label="ALTERNATE_PROTOCOL_USAGE_NO_RACE"/>
   <int value="1" label="ALTERNATE_PROTOCOL_USAGE_WON_RACE"/>