For #5021: Adds metric for what's new button

app/metrics.yaml

@@ -116,6 +116,20 @@ events:
     notification_emails:
     - fenix-core@mozilla.com
     expires: "2020-03-01"
+  whats_new_tapped:
+    type: event
+    description: >
+        A user opened the "what's new" page button
+    extra_keys:
+      source:
+        description: "The location from which the user selected the what's new button. Either 'about' or 'home'"
+    bugs:
+      - 5021
+    data_reviews:
+      - https://github.com/mozilla-mobile/fenix/pull/5090
+    notification_emails:
+      - fenix-core@mozilla.com
+    expires: "2020-03-01"
 
 search_shortcuts:
   opened:

docs/metrics.md

@@ -109,6 +109,19 @@ tracking_protection</td>
         </td>
         <td>2020-03-01</td>
     </tr>
+    <tr>
+       <td>whats_new_tapped</td>
+       <td>event</td>
+       <td>A user opened the "what's new" page button</td>
+       <td><a href="https://github.com/mozilla-mobile/fenix/pull/5090">link</a></td>
+       <td>
+           <table>
+                <tr><td>source</td><td>The location from which the user selected the what's new button. Either 'about' or 'home'</td>
+                </tr>
+            </table>
+        </td>
+        <td>2020-03-01</td>
+    </tr>
 </table>
 </pre>