[SPDY] Add histograms for flow control stalls

tools/metrics/histograms/histograms.xml

 <!--
 Copyright 2013 The Chromium Authors. All rights reserved.
 Use of this source code is governed by a BSD-style license that can be
 found in the LICENSE file.
 -->
 
 <!--
 This file is used to generate a comprehensive list of Chrome histograms along
 with a detailed description for each histogram.
 
@@ skipping 1911 matching lines @@
   </obsolete>
   <summary>
     The counts of the type of sockets returned by the SOCKS pool.
   </summary>
 </histogram>
 
 <histogram name="Net.SpdyConnectionLatency" units="milliseconds">
   <summary>Time from when the Connect() starts until it completes.</summary>
 </histogram>
 
+<histogram name="Net.SpdyFrameStreamAndSessionFlowControlState"
+    enum="SpdyFrameFlowControlState">
+  <summary>
+    The counts of the flow control state of each frame (with stream and session
+    flow control on).
+  </summary>
+</histogram>
+
+<histogram name="Net.SpdyFrameStreamFlowControlState"
+    enum="SpdyFrameFlowControlState">
+  <summary>
+    The counts of the flow control state of each frame (with stream flow control
+    on).
+  </summary>
+</histogram>
+
 <histogram name="Net.SpdyIPPoolDomainMatch" enum="SpdyIPPoolDomainMatch"
     units="count">
   <summary>
     Status of checking if a SPDY domain can handle a IP match.  If a match is
     found, we successfully used the IP Pooling.  If a match is not found, we
     could have used IP Pooling, except the TLS Cert didn't match the IP-pooled
     domain.
   </summary>
 </histogram>
 
@@ skipping 3618 matching lines @@
   <int value="3" label="socks connections"/>
   <int value="4" label="ssl connections"/>
 </enum>
 
 <enum name="SocketStreamProtocolType" type="int">
   <int value="0" label="unknown"/>
   <int value="1" label="ws"/>
   <int value="2" label="wss"/>
 </enum>
 
+<enum name="SpdyFrameFlowControlState" type="int">
+  <int value="0" label="Send not stalled"/>
+  <int value="1" label="Send stalled by stream"/>
+  <int value="2" label="Send stalled by session"/>
+  <int value="3" label="Send stalled by stream and session"/>
+</enum>
+
 <enum name="SpdyIPPoolDomainMatch" type="int">
   <int value="0" label="mismatch"/>
   <int value="1" label="match"/>
 </enum>
 
 <enum name="SpdyProtocolErrorDetails" type="int">
   <int value="0" label="No error"/>
   <int value="1" label="Invalid Control Frame"/>
   <int value="2" label="Control Frame Payload Too Large"/>
   <int value="3" label="Zlib Init Failure"/>
@@ skipping 1116 matching lines @@
 <fieldtrial name="SSLResumption">
   <group name="Resume_Handshake" label="Session Resumption"/>
   <group name="Full_Handshake" label="Full"/>
   <affected-histogram name="Net.SSL_Connection_Latency"/>
   <affected-histogram name="Net.SSL_Connection_Latency_Google"/>
 </fieldtrial>
 
 </fieldtrials>
 
 </histogram-configuration>