Add detailed histograms for DownloadProtectionService URLFetcher errors.

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 12375 matching lines @@
 </histogram>
 
 <histogram name="SB2.UpdateSize" units="bytes">
   <summary>The size of all the chunk URLs in an update response.</summary>
 </histogram>
 
 <histogram name="SB2.UpdateUrls">
   <summary>The number of chunk URLs in an update response.</summary>
 </histogram>
 
+<histogram name="SBClientDownload.CheckDownloadRequestNetError"

[mmenke, 2013/07/24 14:26:50]

nit:  Think the "Check" isn't needed.  This is a histogram of just the
DownloadRequestNetError codes.  Check doesn't seem to add anything.  Or it is
just for sorting purposes?

[mattm, 2013/07/24 22:39:27]

Mostly it was to sort it near the CheckDownloadStats histogram, but I see there
is also a DownloadRequestDuration histogram, so I guess the shorter form would
be fine too.

+    enum="NetErrorCodes">
+  <summary>
+    For CheckClientDownloadRequest URLFetchers with failed status, the net error
+    code.
+  </summary>
+</histogram>
+
+<histogram name="SBClientDownload.CheckDownloadRequestResponseCode">
+  <summary>
+    For CheckClientDownloadRequest URLFetchers with successful status, the HTTP
+    response code that was received.
+  </summary>
+</histogram>
+
+<histogram name="SBClientDownload.CheckDownloadRequestStatus"
+    enum="URLRequestStatus">
+  <summary>
+    The URLRequestStatus value for CheckClientDownloadRequest URLFetcher
+    completion.
+  </summary>
+</histogram>
+
 <histogram name="SBClientDownload.CheckDownloadStats"
     enum="SBClientDownloadCheckDownloadStats">
   <summary>
     Records a histogram of the reason why downloads are marked as being
     malicious or clean by the improved SafeBrowsing binary download protection.
   </summary>
 </histogram>
 
 <histogram name="SBClientDownload.DownloadExtensions"
     enum="SBClientDownloadExtensions">
@@ skipping 8791 matching lines @@
   <int value="35" label="kErrorCodeOmahaUpdateIgnoredPerPolicy"/>
   <int value="36" label="kErrorCodeOmahaUpdateDeferredPerPolicy"/>
   <int value="37" label="kErrorCodeOmahaErrorInHTTPResponse"/>
   <int value="38" label="kErrorCodeDownloadOperationHashMissingError"/>
   <int value="39" label="kErrorCodeDownloadMetadataSignatureMissingError"/>
   <int value="40" label="kErrorCodeOmahaUpdateDeferredForBackoff"/>
   <int value="41" label="kErrorCodePostinstallPowerwashError"/>
   <int value="42" label="kErrorCodeUpdateCanceledByChannelChange"/>
 </enum>
 
+<enum name="URLRequestStatus" type="int">
+  <int value="0" label="SUCCESS"/>
+  <int value="1" label="IO_PENDING"/>
+  <int value="2" label="CANCELLED"/>
+  <int value="3" label="FAILED"/>
+</enum>
+
 <enum name="UrlResolutionResult" type="int">
   <int value="0" label="Absolute URL"/>
   <int value="1" label="Resolutions Differ"/>
   <int value="2" label="Resolutions Agree"/>
 </enum>
 
 <enum name="URLSchemeForHistogram" type="int">
   <int value="0" label="kUnknownURLScheme"/>
   <int value="1" label="kMissingURLScheme"/>
   <int value="2" label="kHttpURLScheme"/>
@@ skipping 2232 matching lines @@
   <group name="Disabled" label="Neither extra webstore link is visible"/>
   <group name="FooterLink" label="Link in bottom right of footer"/>
   <group name="PlusIcon" label="Plus icon in apps page"/>
   <affected-histogram name="Extensions.AppLaunch"/>
   <affected-histogram name="NewTabPage.DefaultPageType"/>
 </fieldtrial>
 
 </fieldtrials>
 
 </histogram-configuration>