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

components/autofill/core/browser/autofill_metrics.cc

Index: components/autofill/core/browser/autofill_metrics.cc
diff --git a/components/autofill/core/browser/autofill_metrics.cc b/components/autofill/core/browser/autofill_metrics.cc
index c016c6bcec3fc8141e2b67afeef17c01edbba3f4..69dd4f13111e9f4e75acf8a2a8c4db32b466c08a 100644
--- a/components/autofill/core/browser/autofill_metrics.cc
+++ b/components/autofill/core/browser/autofill_metrics.cc
@@ -565,6 +565,14 @@ void AutofillMetrics::FormEventLogger::OnDidFillSuggestion(
   }
 }
 
+void AutofillMetrics::FormEventLogger::OnWillSubmitForm() {
+  // Not logging this kind of form if we haven't logged a user interaction.
+  if (!has_logged_interacted_)
+    return;
+
+  Log(AutofillMetrics::FORM_EVENT_WILL_SUBMIT);

[Ilya Sherman, 2015/03/18 22:42:10]

Should this event be logged only once, as below?

[Mathieu, 2015/03/23 15:24:02]

+walter

I wanted to capture all OnWillSubmit events (possibly AJAX submissions) before
the page navigated. I'm not sure why there is logic to avoid logging
OnFormSubmitted twice. Perhaps walter can advise?

[Walter Cacau, 2015/03/23 19:06:37]

The idea was that we were tracking the basic user flow from:

INTERACT -> SHOW SUGGESTION -> SELECT/FILL SUGGESTION -> SUBMIT
For that, we wanted it to be counted only once per page load.

What is the indent in capturing the FORM_EVENT_WILL_SUBMIT? It may make sense to
create also a FORM_EVENT_WILL_SUBMIT_[CASE]_ONCE if we think there are quite a
few forms that simply submit with ajax without us being able to detect the user
click.

+}
+
 void AutofillMetrics::FormEventLogger::OnDidSubmitForm() {
   // Not logging this kind of form if we haven't logged a user interaction.
   if (!has_logged_interacted_)