Show password generation pop-up after page refresh.

Password generation agent assumes that navigation to a new page or page
refresh will clear the form cache and re-query the autofill server. This
assumption broke after http://crrev.com/ffc78e28 started ignoring page
refresh. The result was unavailability of the password generation pop-up
after page refresh.

This patch restores the previous behavior of clearing the form cache on
page refresh. This triggers re-querying of the autofill server and
correctly showing password generation pop-ups.

BUG=530569
TEST=Open facebook.com, refresh, password generation should be available.

Review URL: https://codereview.chromium.org/1392633002

Cr-Commit-Position: refs/heads/master@{#352958}

components/autofill/content/renderer/autofill_agent.cc

@@ -223,7 +223,8 @@ void AutofillAgent::DidCommitProvisionalLoad(bool is_new_navigation,
 
   if (is_same_page_navigation) {
     OnSamePageNavigationCompleted();
-  } else if (is_new_navigation) {
+  } else {
+    // Navigation to a new page or a page refresh.
     form_cache_.Reset();
     submitted_forms_.clear();
     last_interacted_form_.reset();