[Payment Request] Incomplete item shouldn't appear as selected when tapped.

ios/chrome/browser/ui/payments/payment_request_selector_view_controller.mm

 // Copyright 2017 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.
 
 #import "ios/chrome/browser/ui/payments/payment_request_selector_view_controller.h"
 
 #include "base/mac/foundation_util.h"
 #include "components/strings/grit/components_strings.h"
 #import "ios/chrome/browser/ui/autofill/cells/status_item.h"
 #import "ios/chrome/browser/ui/collection_view/cells/MDCCollectionViewCell+Chrome.h"
@@ skipping 243 matching lines @@
             (paymentRequestSelectorViewController:didSelectItemAtIndexForEditing
                                                     :)]) {
       [self.delegate paymentRequestSelectorViewController:self
                            didSelectItemAtIndexForEditing:index];
     }
     return;
   }
 
   switch (item.type) {
     case ItemTypeSelectableItem: {
-      // Update the currently selected cell, if any.
-      if (self.dataSource.selectedItemIndex != NSUIntegerMax) {
-        DCHECK(self.dataSource.selectedItemIndex <
-               [[self.dataSource selectableItems] count]);
-        CollectionViewItem<PaymentsIsSelectable>* oldSelectedItem =
-            [[self.dataSource selectableItems]
-                objectAtIndex:self.dataSource.selectedItemIndex];
-        oldSelectedItem.accessoryType = MDCCollectionViewCellAccessoryNone;
-        [self reconfigureCellsForItems:@[ oldSelectedItem ]];
-      }
-
-      // Update the newly selected cell.
       CollectionViewItem<PaymentsIsSelectable>* newSelectedItem =
           reinterpret_cast<CollectionViewItem<PaymentsIsSelectable>*>(item);
-      newSelectedItem.accessoryType = MDCCollectionViewCellAccessoryCheckmark;
-      [self reconfigureCellsForItems:@[ newSelectedItem ]];
-
+      // Update the currently selected and the newly selected cells only if the
+      // newly selected cell corresponds to a complete item and can be selected.
+      if (newSelectedItem.isComplete) {
+        // Update the currently selected cell, if any.
+        if (self.dataSource.selectedItemIndex != NSUIntegerMax) {
+          DCHECK(self.dataSource.selectedItemIndex <
+                 [[self.dataSource selectableItems] count]);
+          CollectionViewItem<PaymentsIsSelectable>* oldSelectedItem =
+              [[self.dataSource selectableItems]
+                  objectAtIndex:self.dataSource.selectedItemIndex];
+          oldSelectedItem.accessoryType = MDCCollectionViewCellAccessoryNone;
+          [self reconfigureCellsForItems:@[ oldSelectedItem ]];
+        }
+        // Update the newly selected cell.
+        newSelectedItem.accessoryType = MDCCollectionViewCellAccessoryCheckmark;
+        [self reconfigureCellsForItems:@[ newSelectedItem ]];
+      }
       // Notify the delegate of the selection.
       NSUInteger index =
           [self.collectionViewModel indexInItemTypeForIndexPath:indexPath];
       DCHECK(index < [[self.dataSource selectableItems] count]);
       [self.delegate paymentRequestSelectorViewController:self
                                      didSelectItemAtIndex:index];
       break;
     }
     case ItemTypeAddItem: {
       if ([self.delegate
@@ skipping 30 matching lines @@
     hidesInkViewAtIndexPath:(NSIndexPath*)indexPath {
   NSInteger type = [self.collectionViewModel itemTypeForIndexPath:indexPath];
   if (type == ItemTypeHeader) {
     return YES;
   } else {
     return NO;
   }
 }
 
 @end