Add histograms for MouseEventPrefetch.Mouse*

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 1066 matching lines @@
 
 <histogram name="MemoryAndroid.NotificationForeground"
     enum="AndroidMemoryNotificationForeground">
   <summary>
     Memory notifications delivered through system callbacks to Chrome while in
     the foreground - we count LowMemory notification vs particular levels of
     TrimMemory foreground notification.
   </summary>
 </histogram>
 
+<histogram name="MouseEventPrefetch.MouseDownDuration_Click" units="ms">
+  <summary>
+    Measures the time elapsed between when the user mousedown-ed a link and when
+    the user clicked a link.
+  </summary>
+</histogram>
+
+<histogram name="MouseEventPrefetch.MouseDownFollowedByClick"
+    enum="MouseEventFollowedByClick">
+  <summary>
+    Caught: The number of mousedown events detected prior to HTML anchor-tag
+    links' default click event handler. Miss: The number of HTML anchor-tag
+    links' default click events without prior mousedown events.

[Ilya Sherman, 2013/05/07 08:52:23]

Optional nit: I think this description would be easier to understand if it were
worded something more like:

"For each click handled by an HTML anchor tag link, whether Blink [or some other
system?] saw a mousedown event preceding it.  This is only measured for clicks
handled by the anchor tag's default click event handler."

+  </summary>
+</histogram>
+
+<histogram name="MouseEventPrefetch.MouseDowns">
+  <summary>
+    The number of mousedown events detected at HTML anchor-tag links' default
+    event handler.
+  </summary>
+</histogram>
+
+<histogram name="MouseEventPrefetch.MouseOverDuration_Click" units="ms">
+  <summary>
+    Measures the time elapsed between when the user mouseover-ed a link and when
+    the user clicked a link.
+  </summary>
+</histogram>
+
+<histogram name="MouseEventPrefetch.MouseOverDuration_NoClick" units="ms">
+  <summary>
+    Measures the time elapsed between when the user mouseover-ed a link and when
+    the user mouseout-ed a link without click.
+  </summary>
+</histogram>
+
+<histogram name="MouseEventPrefetch.MouseOvers">
+  <summary>
+    The number of mouseover events detected at HTML anchor-tag links' default
+    event handler.
+  </summary>
+</histogram>
+
 <histogram name="Navigation.MainFrameScheme" enum="NavigationScheme">
   <summary>The scheme of the URL for each main-frame navigation.</summary>
 </histogram>
 
 <histogram name="Net.AsyncResourceHandler_PendingDataCount">
   <summary>
     The count of unacknowledged ResourceMsg_DataReceived messages.  This message
     is sent once per chunk of data read from the network.
   </summary>
 </histogram>
@@ skipping 8253 matching lines @@
   <int value="6" label="LINK_LOAD_RELOAD">JS/link directed reload</int>
   <int value="7" label="LINK_LOAD_CACHE_STALE_OK">
     back/forward or encoding change
   </int>
   <int value="8" label="LINK_LOAD_CACHE_ONLY">
     Allow stale data (avoid doing a re-post)
   </int>
   <int value="9" label="PRERENDER_LOAD">Speculative prerendering of a page</int>
 </enum>
 
+<enum name="MouseEventFollowedByClick" type="int">
+  <int value="0" label="Caught_event_before_click"/>

[Ilya Sherman, 2013/05/07 08:52:23]

nit: No need for underscores; you can use spaces.  This is a human-readable
label.

+  <int value="1" label="Miss_event_before_click"/>

[Ilya Sherman, 2013/05/07 08:52:23]

Ditto.  Also, probably "Missed" rather than "Miss"

+</enum>
+
 <enum name="NavigationScheme" type="int">
   <int value="0" label="(Unknown)"/>
   <int value="1" label="http"/>
   <int value="2" label="https"/>
   <int value="3" label="file"/>
   <int value="4" label="ftp"/>
   <int value="5" label="data"/>
   <int value="6" label="javascript"/>
   <int value="7" label="about"/>
   <int value="8" label="chrome"/>
@@ skipping 2613 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>