Added two histograms to measure the impact of persisting 1000 alternate

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 958ecc96c492a8f18ba4d717a5afe10f57c6acbe..f1192e9be1cf6de9a8b53d4381f0af64af4a675a 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -11225,6 +11225,26 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Net.AlternateProtocolUsage.1000Truncated"
+    enum="AlternateProtocolUsage">
+  <owner>rch@chromium.org</owner>
+  <summary>
+    Breakdown of how requests which could potentially make use of an alternate
+    protocol use or don't use the protocol. Loaded data for 1000 servers and we
+    have persisted 1000 MRU servers.
+  </summary>
+</histogram>
+
+<histogram name="Net.AlternateProtocolUsage.200Truncated"
+    enum="AlternateProtocolUsage">
+  <owner>rch@chromium.org</owner>
+  <summary>
+    Breakdown of how requests which could potentially make use of an alternate
+    protocol use or don't use the protocol. Loaded data for 200 servers and we
+    have persisted 1000 MRU servers.
+  </summary>
+</histogram>
+
 <histogram name="Net.AsyncResourceHandler_PendingDataCount">
   <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
   <summary>