Add HTTP/2 draft-15 values to SSLProtocolNegotiation.

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 c3b487fc0035c912a7cfaa9b11284d53d75e2ee0..a1bdde709bf81b521f2907b293c71376eb55c9a9 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -54996,18 +54996,21 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="101" label="ALPN, SPDY 3.0"/>
   <int value="102" label="ALPN, SPDY 3.1"/>
   <int value="103" label="ALPN, HTTP/2 draft-14"/>
+  <int value="104" label="ALPN, HTTP/2 draft-15"/>
   <int value="200" label="ALPN, QUIC/1 + SPDY/3"/>
   <int value="501" label="NPN, HTTP/1.1"/>
   <int value="600" label="NPN, SPDY 2.0"/>
   <int value="601" label="NPN, SPDY 3.0"/>
   <int value="602" label="NPN, SPDY 3.1"/>
   <int value="603" label="NPN, HTTP/2 draft-14"/>
+  <int value="604" label="NPN, HTTP/2 draft-15"/>
   <int value="700" label="NPN, QUIC/1 + SPDY/3"/>
   <int value="1001" label="NPN, fallback to HTTP/1.1"/>
   <int value="1100" label="NPN, fallback to SPDY 2.0"/>
   <int value="1101" label="NPN, fallback to SPDY 3.0"/>
   <int value="1102" label="NPN, fallback to SPDY 3.1"/>
   <int value="1103" label="NPN, fallback to HTTP/2 draft-14"/>
+  <int value="1104" label="NPN, fallback to HTTP/2 draft-15"/>
   <int value="1200" label="NPN, fallback to QUIC/1 + SPDY/3"/>
 </enum>