Reland of Set user agent type of transient item the same as pending item

ios/web/navigation/navigation_manager_impl.mm

Index: ios/web/navigation/navigation_manager_impl.mm
diff --git a/ios/web/navigation/navigation_manager_impl.mm b/ios/web/navigation/navigation_manager_impl.mm
index da2ae03a14d715f438312e472af75142eecc141b..bc56b897bcbbc4ba655d09986353d82b9084796d 100644
--- a/ios/web/navigation/navigation_manager_impl.mm
+++ b/ios/web/navigation/navigation_manager_impl.mm
@@ -170,6 +170,20 @@ bool AreURLsInPageNavigation(const GURL& existing_url, const GURL& new_url) {
   delegate_->GetWebState()->OpenURL(params);
 }
 
+void NavigationManagerImpl::AddTransientItem(const GURL& url) {
+  [session_controller_ addTransientItemWithURL:url];
+
+  // TODO(crbug.com/676129): Add a DCHECK that pending item should always exists

[Eugene But (OOO till 7-30), 2017/04/05 22:05:39]

There is no need for DCHECK, because when crbug.com/676129 is fined then code
should look like this:

GetPendingItem()->GetUserAgentType() // no need to DCHECK something that will
crash anyway. In TODO comment, please explain that |item| can be null because of
the bug and the workaround should be removed.

+  // when the bug is fixed, because transient item is only supposed to be added
+  // for pending non-app-specific loads.
+  NavigationItem* item = GetPendingItem();
+  if (!item)
+    item = GetLastCommittedNonAppSpecificItem();
+  DCHECK(!item || item->GetUserAgentType() != UserAgentType::NONE);
+  if (item)

[Eugene But (OOO till 7-30), 2017/04/05 22:05:39]

When can |item| be null?

+    GetTransientItem()->SetUserAgentType(item->GetUserAgentType());
+}
+
 void NavigationManagerImpl::AddPendingItem(
     const GURL& url,
     const web::Referrer& referrer,