Add two new WebSocket histograms to track adoption of the permessage-deflate extension.

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 0db903d22f5b986c215e7c8ede5951f4db035bd4..31c7beac568a7c447db48ded6aab1b9f23707bd7 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -8809,6 +8809,22 @@ other types of suffix sets.
   </summary>
 </histogram>
 
+<histogram name="WebCore.WebSocket.HandshakeResult"
+    enum="WebSocketHandshakeResult">
+  <summary>
+    Count the number of WebSocket handshake for each result. Use this histogram
+    as a baseline for investigating feature usage counters.
+  </summary>
+</histogram>
+
+<histogram name="WebCore.WebSocket.PerMessageDeflateContextTakeOverMode"
+    enum="WebSocketPerMessageDeflateContextTakeOverMode">
+  <summary>
+    Count the number of WebSockets that accepted permessage-deflate extension
+    for each context take over mode.
+  </summary>
+</histogram>
+
 <histogram name="WebCore.XHR.send.ArrayBufferOrView"
     enum="XMLHttpRequestSendArrayBufferOrView">
   <summary>
@@ -13172,6 +13188,18 @@ other types of suffix sets.
   <int value="11" label="Require phone number"/>
 </enum>
 
+<enum name="WebSocketHandshakeResult" type="int">
+  <int value="0" label="Incomplete"/>
+  <int value="1" label="Normal"/>
+  <int value="2" label="Failed"/>
+  <int value="3" label="Connected"/>
+</enum>
+
+<enum name="WebSocketPerMessageDeflateContextTakeOverMode" type="int">
+  <int value="0" label="DoNotTakeOverContext"/>
+  <int value="1" label="TakeOverContext"/>
+</enum>
+
 <enum name="WiFiReasonCode" type="int">
   <int value="0" label="kReasonReserved0"/>
   <int value="1" label="kReasonCodeUnspecified"/>