Copy signature to PasswordFieldPrediction.

Bug: 959776
Change-Id: I135f13de7b9cad69525db3d2d91b991c0e477a01
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1944858Reviewed-by: Vasilii Sukhanov <vasilii@chromium.org>
Commit-Queue: Vadym Doroshenko <dvadym@chromium.org>
Cr-Commit-Position: refs/heads/master@{#720480}

components/password_manager/core/browser/form_parsing/password_field_prediction.cc

@@ -88,6 +88,7 @@ FormPredictions ConvertToFormPredictions(int driver_id,
 
     field_predictions.emplace_back();
     field_predictions.back().renderer_id = field->unique_renderer_id;
+    field_predictions.back().signature = field->GetFieldSignature();
     field_predictions.back().type = server_type;
     field_predictions.back().may_use_prefilled_placeholder =
         may_use_prefilled_placeholder;

components/password_manager/core/browser/form_parsing/password_field_prediction_unittest.cc

@@ -89,6 +89,8 @@ TEST(FormPredictionsTest, ConvertToFormPredictions) {
     EXPECT_EQ(test_fields[i].expected_type, actual_prediction.type);
     EXPECT_EQ(test_fields[i].may_use_prefilled_placeholder,
               actual_prediction.may_use_prefilled_placeholder);
+    EXPECT_EQ(form_structure.field(i)->GetFieldSignature(),
+              actual_prediction.signature);
   }
 }