Omnibox: Add UMA Histogram to Dashboard

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 2385 matching lines @@
 </histogram>
 
 <histogram name="Net.Wifi.LbsLatency" units="milliseconds">
   <summary>The time that a request to Location Based Services takes.</summary>
 </histogram>
 
 <histogram name="Net.Wifi.ScanLatency" units="milliseconds">
   <summary>The time that a Wi-fi scan takes.</summary>
 </histogram>
 
+<histogram name="Omnibox.EnteredKeywordMode" enum="OmniboxEnteredKeywordMode">
+  <summary>
+    The number of times users enter keyword hint mode &quot;Search ___
+    for:&quot; and how.
+  </summary>
+</histogram>
+
 <histogram name="PlatformFile.UnknownCreateFileErrors" units="code">
   <summary>
     Errors returned by CreateFile on windows that PlatformFileError doesn't yet
     support.
   </summary>
 </histogram>
 
 <histogram name="PLT.Abandoned" enum="Abandoned">
   <summary>
     Distribution of actual finished pages, vs abandoned pages, where we needed
@@ skipping 2244 matching lines @@
   <int value="1" label="non-speculative, never used"/>
   <int value="2" label="non-speculative and used"/>
   <int value="3" label="omnibox never connected"/>
   <int value="4" label="omnibox never used"/>
   <int value="5" label="omnibox and used"/>
   <int value="6" label="subresource never connected"/>
   <int value="7" label="subresource never used"/>
   <int value="8" label="subresource and used"/>
 </enum>
 
+<enum name="OmniboxEnteredKeywordMode" type="int">
+  <int value="0" label="via tab"/>
+  <int value="1" label="via space at end"/>
+  <int value="2" label="via space in middle"/>
+</enum>
+
 <enum name="OSAgnosticErrno" type="int">
   <summary>Errno values with the same meanings on Mac/Win/Linux.</summary>
   <int value="0" label="0">No error</int>
   <int value="1" label="EPERM">Operation not permitted</int>
   <int value="2" label="ENOENT">No such file or directory</int>
   <int value="3" label="ESRCH">No such process</int>
   <int value="4" label="EINTR">Interrupted function call</int>
   <int value="5" label="EIO">Input/output error</int>
   <int value="6" label="ENXIO">No such device or address</int>
   <int value="7" label="E2BIG">Arg list too long</int>
@@ skipping 699 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>