[Autofill] Add FormEvent logging for "will submit form".

components/autofill/core/browser/autofill_metrics.h

Index: components/autofill/core/browser/autofill_metrics.h
diff --git a/components/autofill/core/browser/autofill_metrics.h b/components/autofill/core/browser/autofill_metrics.h
index 88419a501a1d73047e5a1119548819978d5e2dee..dd92d1192818f3d5176cc5b68abbfbb8b0ddb8ba 100644
--- a/components/autofill/core/browser/autofill_metrics.h
+++ b/components/autofill/core/browser/autofill_metrics.h
@@ -281,6 +281,11 @@ class AutofillMetrics {
     FORM_EVENT_MASKED_SERVER_CARD_SUGGESTION_SELECTED,
     // Same as above but only triggered once per page load.
     FORM_EVENT_MASKED_SERVER_CARD_SUGGESTION_SELECTED_ONCE,
+    // An autofillable form is about to be submitted. If the submission is not
+    // interrupted by JavaScript, the "form submitted" events below will also be

[Ilya Sherman, 2015/03/23 20:58:16]

nit: "below" -> "above"

[Mathieu, 2015/03/23 21:11:28]

Done.

+    // logged. Triggered once per page load.

[Ilya Sherman, 2015/03/23 20:58:17]

nit: "once" -> "at most once"

[Mathieu, 2015/03/23 21:11:28]

Done.

+    FORM_EVENT_WILL_SUBMIT_ONCE,
+
     NUM_FORM_EVENTS,
   };
 
@@ -546,7 +551,9 @@ class AutofillMetrics {
 
     void OnDidFillSuggestion(const AutofillProfile& profile);
 
-    void OnDidSubmitForm();
+    void OnWillSubmitForm();
+
+    void OnFormSubmitted();
 
    private:
     void Log(FormEvent event) const;
@@ -558,6 +565,7 @@ class AutofillMetrics {
     bool has_logged_suggestions_shown_;
     bool has_logged_masked_server_card_suggestion_selected_;
     bool has_logged_suggestion_filled_;
+    bool has_logged_will_submit_;
     bool has_logged_submitted_;
     bool logged_suggestion_filled_was_server_data_;
     bool logged_suggestion_filled_was_masked_server_card_;