Reject unadvertised encodings

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 17e33a9223f579b13076fb64634f3ad987a5883d..bc394591e16ee5af82652f3173ca98a9879ed251 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -103862,6 +103862,17 @@ from previous Chrome versions.
   <int value="5" label="SDCHPossible"/>
   <int value="6" label="Invalid"/>
   <int value="7" label="None"/>
+  <int value="8" label="Rejected">
+    Unlike other values, this one is reported from HttpNetworkTransaction in a
+    case when an unadvertised, but known encoding appears in a
+    &quot;Content-Encoding&quot; header, and is thus not comparable with the
+    other values, which are potentially returned from cached entries.
+  </int>
+  <int value="9" label="Unknown">
+    Reported from URLRequestHttpJob::SetUpSourceStream when an unknown encoding
+    appears in a &quot;Content-Encoding&quot; header. Despite being reported in
+    this histogram, this does not cause a CONTENT_DECODING_FAILED error.
+  </int>
 </enum>
 
 <enum name="NetInternalsUiFeature" type="int">