[Nav Experiment] Set back-forward bit in NavigationItem transition type.

Fix a bug where WKBasedNavigationManager is not setting the
ui::PAGE_TRANSITION_FORWARD_BACK bit in an existing NavigationItem in
history navigation.

The legacy navigation manager doesn't set this bit for same-document
back-forward navigation. This seems to be a bug, but will be fixed in
a separate CL to make possible bisecting easier.

Bug: 798832
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I2967256a32027384e16b03c24fdc0ee899a3d61d
Reviewed-on: https://chromium-review.googlesource.com/849352Reviewed-by: Eugene But <eugenebut@chromium.org>
Commit-Queue: Danyao Wang <danyao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#526844}

ios/web/navigation/navigation_manager_impl_unittest.mm

@@ -2227,6 +2227,8 @@ TEST_P(NavigationManagerTest, GoToIndexDifferentDocument) {
 
   EXPECT_EQ(1, navigation_manager()->GetLastCommittedItemIndex());
   EXPECT_EQ(-1, navigation_manager()->GetPendingItemIndex());
+  EXPECT_FALSE(navigation_manager()->GetItemAtIndex(0)->GetTransitionType() &
+               ui::PAGE_TRANSITION_FORWARD_BACK);
 
   EXPECT_CALL(navigation_manager_delegate(), RecordPageStateInNavigationItem());
   EXPECT_CALL(navigation_manager_delegate(), ClearTransientContent());
@@ -2240,6 +2242,8 @@ TEST_P(NavigationManagerTest, GoToIndexDifferentDocument) {
   }
 
   navigation_manager()->GoToIndex(0);
+  EXPECT_TRUE(navigation_manager()->GetItemAtIndex(0)->GetTransitionType() &
+              ui::PAGE_TRANSITION_FORWARD_BACK);
 
   if (GetParam() == TEST_LEGACY_NAVIGATION_MANAGER) {
     // Since LoadCurrentItem() is noop in test, we can only verify that the
@@ -2270,6 +2274,8 @@ TEST_P(NavigationManagerTest, GoToIndexSameDocument) {
 
   EXPECT_EQ(1, navigation_manager()->GetLastCommittedItemIndex());
   EXPECT_EQ(-1, navigation_manager()->GetPendingItemIndex());
+  EXPECT_FALSE(navigation_manager()->GetItemAtIndex(0)->GetTransitionType() &
+               ui::PAGE_TRANSITION_FORWARD_BACK);
 
   EXPECT_CALL(navigation_manager_delegate(), RecordPageStateInNavigationItem());
   EXPECT_CALL(navigation_manager_delegate(), ClearTransientContent());
@@ -2282,6 +2288,12 @@ TEST_P(NavigationManagerTest, GoToIndexSameDocument) {
   }
 
   navigation_manager()->GoToIndex(0);
+  // Preserve the existing behavior of legacy navigation manager for change
+  // management, even though it seems like a bug that the back-forward
+  // transition bit is not set for same-document history navigation.
+  EXPECT_EQ(GetParam() == TEST_WK_BASED_NAVIGATION_MANAGER,
+            (navigation_manager()->GetItemAtIndex(0)->GetTransitionType() &
+             ui::PAGE_TRANSITION_FORWARD_BACK) > 0);
 
   if (GetParam() == TEST_LEGACY_NAVIGATION_MANAGER) {
     EXPECT_EQ(0, navigation_manager()->GetLastCommittedItemIndex());
@@ -2309,6 +2321,8 @@ TEST_P(NavigationManagerTest, GoToIndexDifferentUserAgentType) {
 
   EXPECT_CALL(navigation_manager_delegate(), WillChangeUserAgentType());
   navigation_manager()->GoToIndex(0);
+  EXPECT_TRUE(navigation_manager()->GetItemAtIndex(0)->GetTransitionType() &
+              ui::PAGE_TRANSITION_FORWARD_BACK);
 }
 
 TEST_P(NavigationManagerTest, LoadIfNecessary) {

ios/web/navigation/wk_based_navigation_manager_impl.mm

@@ -456,6 +456,9 @@ NavigationItemImpl* WKBasedNavigationManagerImpl::GetTransientItemImpl() const {
 
 void WKBasedNavigationManagerImpl::FinishGoToIndex(int index) {
   DiscardNonCommittedItems();
+  NavigationItem* item = GetItemAtIndex(index);
+  item->SetTransitionType(ui::PageTransitionFromInt(
+      item->GetTransitionType() | ui::PAGE_TRANSITION_FORWARD_BACK));
   WKBackForwardListItem* wk_item = GetWKItemAtIndex(index);
   DCHECK(wk_item);
   [delegate_->GetWebViewNavigationProxy() goToBackForwardListItem:wk_item];