Match histogram name to code

This histogram *should* be named OptOuts, but I gave it the wrong name
in the code. For now, I just want to be able to see it in UMA.

Review-Url: https://codereview.chromium.org/2875073002
Cr-Commit-Position: refs/heads/master@{#471094}

tools/metrics/histograms/histograms.xml

@@ -42462,23 +42462,23 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
-<histogram name="NewTabPage.ContentSuggestions.Notifications.Impressions"
-    enum="ContentSuggestionsNotificationsImpression">
+<histogram name="NewTabPage.ContentSuggestions.Notifications.AutoOptOuts"
+    enum="ContentSuggestionsNotificationsOptOut">
   <owner>sfiera@chromium.org</owner>
   <summary>
-    Android: The number of notifications that were shown, keyed by category. One
-    bucket counts the server-provided ARTICLES category; the other counts
-    everything else.
+    Android: The number of times a user opted out, keyed by method: IMPLICIT
+    (user ignored enough notifications consecutively that we think they're not
+    interested), or EXPLICIT (via explicit setting).
   </summary>
 </histogram>
 
-<histogram name="NewTabPage.ContentSuggestions.Notifications.OptOuts"
-    enum="ContentSuggestionsNotificationsOptOut">
+<histogram name="NewTabPage.ContentSuggestions.Notifications.Impressions"
+    enum="ContentSuggestionsNotificationsImpression">
   <owner>sfiera@chromium.org</owner>
   <summary>
-    Android: The number of times a user opted out, keyed by method: IMPLICIT
-    (user ignored enough notifications consecutively that we think they're not
-    interested), or EXPLICIT (via explicit setting).
+    Android: The number of notifications that were shown, keyed by category. One
+    bucket counts the server-provided ARTICLES category; the other counts
+    everything else.
   </summary>
 </histogram>