Add aggregation to InputDelay UKM so that it shows up in UKM dashboard.

Change-Id: Idaa65efb18c2f275d54eb471cf3d3014405fb399
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2033762Reviewed-by: Bryan McQuade <bmcquade@chromium.org>
Commit-Queue: Annie Sullivan <sullivan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#737792}

tools/metrics/ukm/ukm.xml

@@ -4155,6 +4155,18 @@ be describing additional metrics about the same event.
       start of event processing on the main thread for the meaningful input. In
       ms. (go/FirstInputDelay)
     </summary>
+    <aggregation>
+      <history>
+        <index fields="profile.country"/>
+        <index fields="profile.country,profile.system_ram"/>
+        <index fields="profile.is_dominant_version"/>
+        <index fields="profile.is_latest_version"/>
+        <index fields="profile.system_ram"/>
+        <statistics>
+          <quantiles type="std-percentiles"/>
+        </statistics>
+      </history>
+    </aggregation>
   </metric>
 </event>