Disallow showing offline previews on a reload.

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 8df98065368bf0b66dc55c21868b5844da82377e..5496c716ec884674add09927f7904f76c4a26f54 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -98711,6 +98711,9 @@ value.
   <int value="5" label="User is blacklisted for the specific host."/>
   <int value="6" label="The network quality estimate is not available."/>
   <int value="7" label="The network is not slow enough to show previews."/>
+  <int value="8"
+      label="The page was being reloaded and the preview type can not be
+             shown on a reload."/>
 </enum>
 
 <enum name="PreviewsInfoBarAction" type="int">