[Autofill] Return early when no new forms are parsed.

components/autofill/core/browser/autofill_manager_unittest.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <algorithm>
 #include <vector>
 
 #include "base/command_line.h"
 #include "base/format_macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/scoped_vector.h"
 #include "base/prefs/pref_service.h"
 #include "base/run_loop.h"
 #include "base/strings/string16.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
+#include "base/test/histogram_tester.h"
 #include "base/thread_task_runner_handle.h"
 #include "base/time/time.h"
 #include "components/autofill/core/browser/autocomplete_history_manager.h"
 #include "components/autofill/core/browser/autofill_manager.h"
 #include "components/autofill/core/browser/autofill_profile.h"
 #include "components/autofill/core/browser/autofill_test_utils.h"
 #include "components/autofill/core/browser/credit_card.h"
 #include "components/autofill/core/browser/personal_data_manager.h"
 #include "components/autofill/core/browser/popup_item_ids.h"
 #include "components/autofill/core/browser/test_autofill_client.h"
@@ skipping 771 matching lines @@
       form_field->set_server_type(server_types[i]);
     }
 
     UpdateAutofillCount();
   }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(TestFormStructure);
 };
 
+// Test that calling OnFormsSeen with an empty set of forms (such as when
+// reloading a page or when the renderer processes a set of forms but detects
+// no changes) does not load the forms again.
+TEST_F(AutofillManagerTest, OnFormsSeen_Empty) {
+  // Set up our form data.
+  FormData form;
+  test::CreateTestAddressFormData(&form);
+  std::vector<FormData> forms(1, form);
+
+  base::HistogramTester histogram_tester;
+  FormsSeen(forms);
+  histogram_tester.ExpectUniqueSample(
+      "Autofill.UserHappiness", 0 /* FORMS_LOADED */, 1);
+
+  // No more forms, metric is not logged.
+  FormsSeen(std::vector<FormData>{});
+  histogram_tester.ExpectUniqueSample(
+      "Autofill.UserHappiness", 0 /* FORMS_LOADED */, 1);
+}
+
 // Test that we return all address profile suggestions when all form fields are
 // empty.
 TEST_F(AutofillManagerTest, GetProfileSuggestionsEmptyValue) {
   // Set up our form data.
   FormData form;
   test::CreateTestAddressFormData(&form);
   std::vector<FormData> forms(1, form);
   FormsSeen(forms);
 
   const FormFieldData& field = form.fields[0];
@@ skipping 2415 matching lines @@
 
   external_delegate_->CheckSuggestions(
       kDefaultPageID,
       Suggestion("Shawn Smith", "1234 Smith Blvd., Robin Adam Smith Grimes", "",
                  1),
       Suggestion("Adam Smith", "1234 Smith Blvd., Carl Shawn Smith Grimes", "",
                  2));
 }
 
 }  // namespace autofill