Added |lastCommittedURL| and |visibleURL| to Tab's interface.

ios/chrome/browser/tabs/tab.mm

Index: ios/chrome/browser/tabs/tab.mm
diff --git a/ios/chrome/browser/tabs/tab.mm b/ios/chrome/browser/tabs/tab.mm
index 7fa0dbb396e436e9cff3b8cc3a8a6bf5cbff6834..7f18cebaf9fa2814eec777f04b0a49647065d55a 100644
--- a/ios/chrome/browser/tabs/tab.mm
+++ b/ios/chrome/browser/tabs/tab.mm
@@ -631,7 +631,17 @@ - (void)retrieveSnapshot:(void (^)(UIImage*))callback {
 - (const GURL&)url {
   // See note in header; this method should be removed.
   web::NavigationItem* item =
-      [[self navigationManagerImpl]->GetSessionController() currentItem];
+      [self navigationManagerImpl]->GetSessionController().currentItem;
+  return item ? item->GetVirtualURL() : GURL::EmptyGURL();
+}
+
+- (const GURL&)lastCommittedURL {
+  web::NavigationItem* item = self.navigationManager->GetLastCommittedItem();
+  return item ? item->GetVirtualURL() : GURL::EmptyGURL();
+}
+
+- (const GURL&)visibleURL {
+  web::NavigationItem* item = self.navigationManager->GetVisibleItem();
   return item ? item->GetVirtualURL() : GURL::EmptyGURL();
 }