[Autofill] UKM for suggestions polled field.

tools/metrics/ukm/ukm.xml

Index: tools/metrics/ukm/ukm.xml
diff --git a/tools/metrics/ukm/ukm.xml b/tools/metrics/ukm/ukm.xml
index 541f1f6bc6ea3b5166ec6120c58496b55577d051..ad7a01029812a54dbf30d257fcf9164b6a3d2eff 100644
--- a/tools/metrics/ukm/ukm.xml
+++ b/tools/metrics/ukm/ukm.xml
@@ -70,6 +70,35 @@ along with a detailed description for each metric.
   </metric>
 </event>
 
+<event name="Autofill.PollSuggestions">
+  <owner>jiahuiguo@google.com</owner>
+  <summary>
+    Records which field type the suggestions are polled from.
+  </summary>
+  <metric name="HeuristicType">
+    <summary>
+      Field's |ServerFieldType| based on heuristics. See
+      |AutofillField.heuristic_type()|.
+    </summary>
+  </metric>
+  <metric name="HtmlFieldType">
+    <summary>
+      Field's autocomplete field type hint. See |AutofillField.html_type()|.
+    </summary>
+  </metric>
+  <metric name="MillisecondsSinceFormLoaded">
+    <summary>
+      Time since form parse.
+    </summary>
+  </metric>
+  <metric name="ServerType">
+    <summary>
+      Field's |ServerFieldType| returned by server. See
+      |AutofillField.server_type()|.
+    </summary>
+  </metric>
+</event>
+
 <event name="Autofill.SuggestionsShown">
   <owner>csashi@google.com</owner>
   <metric name="MillisecondsSinceFormLoaded">