Adding UMA to track previews opt outs and blacklist eligibility

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 901af086a1fe499284aef6bca38b20847c99bb49..72a75ea0e635bb2955ba6ad16cd7b0d0774fd697 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -48331,6 +48331,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Previews.EligibilityReason.Offline"

[tbansal1, 2016/11/09 17:50:52]

May be name this "Previews.EligibilityReason" and the one below
"Previews.OptOut.UserOptedOut". Then create "Offline" suffix and apply it to
both histograms. Makes it easier to add new suffixes. histogram descriptions
would also need to be updated.

[RyanSturm, 2016/11/09 18:48:29]

I'd prefer to make the change later as we have more consumers of this. It's
straightforward to do.

+    enum="PreviewsEligibilityReason">
+  <owner>ryansturm@chromium.org</owner>
+  <summary>
+    Whether an offline preview was allowed to be shown or the reason the preview
+    could not be shown to the user.
+  </summary>
+</histogram>
+
 <histogram name="Previews.InfoBarAction.LitePage" enum="PreviewsInfoBarAction">
   <owner>bengr@chromium.org</owner>
   <owner>megjablon@chromium.org</owner>
@@ -48377,6 +48386,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Previews.OptOut.UserOptedOut.Offline" units="Boolean">
+  <owner>ryansturm@chromium.org</owner>
+  <summary>
+    True if the user opted out of an offline preview. False if the user did not
+    opt out when a preview was shown.
+  </summary>
+</histogram>
+
 <histogram name="Previews.OriginalContentLength" units="KB">
   <owner>ryansturm@chromium.org</owner>
   <summary>
@@ -96563,6 +96580,17 @@ value.
   <int value="4" label="'Load images' context menu item clicked"/>
 </enum>
 
+<enum name="PreviewsEligibilityReason" type="int">
+  <int value="0" label="Preview Allowed."/>
+  <int value="1" label="Blacklist not created."/>
+  <int value="2" label="Blacklist data not loaded yet from disk."/>
+  <int value="3" label="User opted out of a preview recently."/>
+  <int value="4" label="User is blacklisted for all hosts."/>
+  <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."/>
+</enum>
+
 <enum name="PreviewsInfoBarAction" type="int">
   <int value="0" label="Infobar shown"/>
   <int value="1" label="Infobar 'Load original' clicked"/>