[net] Better StopCaching() handling for HttpCache::Transaction.

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 df5c49d123550c50097d54c0d48ae94c41336e1e..5606a65d06c02d4fb599c17ab5fb4d00e185b2a5 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -14494,6 +14494,13 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="HttpCache.Pattern" enum="HttpCachePattern">
+  <owner>rvargas@chromium.org</owner>
+  <summary>
+    Cache usage pattern recorded for each HttpCache::Transaction.
+  </summary>
+</histogram>
+
 <histogram name="HttpCache.ReadErrorNonRestartable" enum="NetErrorCodes">
   <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
   <summary>Net error results from non-restartable cache read errors.</summary>
@@ -61633,6 +61640,16 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="15" label="Negotiate Secure Server"/>
 </enum>
 
+<enum name="HttpCachePattern" type="int">
+  <int value="0" label="Undefined"/>
+  <int value="1" label="Not Covered"/>
+  <int value="2" label="Not Cached"/>
+  <int value="3" label="Used"/>
+  <int value="4" label="Validated"/>
+  <int value="5" label="Updated"/>
+  <int value="6" label="CantConditionalize"/>
+</enum>
+
 <enum name="HttpHeaderParserEvent" type="int">
   <int value="0" label="PARSER_INVOKED"/>
   <int value="1" label="HTTP_09_RESPONSE"/>