Remove usage of Tab's |url| property from TabModel.

ios/chrome/browser/tabs/tab_model.mm

Index: ios/chrome/browser/tabs/tab_model.mm
diff --git a/ios/chrome/browser/tabs/tab_model.mm b/ios/chrome/browser/tabs/tab_model.mm
index 193dd1f2225c928b458b6e721b8a817aa3b2a4f4..6256932e24718f4af85a42743779b796c75330b9 100644
--- a/ios/chrome/browser/tabs/tab_model.mm
+++ b/ios/chrome/browser/tabs/tab_model.mm
@@ -593,8 +593,14 @@ - (NSSet*)currentlyReferencedExternalFiles {
     return referencedFiles;
   // Check the currently open tabs for external files.
   for (Tab* tab in self) {
-    if (UrlIsExternalFileReference(tab.url)) {
-      NSString* fileName = base::SysUTF8ToNSString(tab.url.ExtractFileName());
+    const GURL& lastCommittedURL = tab.lastCommittedURL;
+    web::NavigationItem* pendingItem =
+        tab.webState->GetNavigationManager()->GetPendingItem();
+    const GURL& pendingURL =
+        pendingItem ? pendingItem->GetURL() : GURL::EmptyGURL();
+    if (UrlIsExternalFileReference(lastCommittedURL) ||
+        UrlIsExternalFileReference(pendingURL)) {
+      NSString* fileName = base::SysUTF8ToNSString(URL.ExtractFileName());

[Eugene But (OOO till 7-30), 2017/05/31 22:43:11]

Does it compile? I can't fine |URL| variable.

[kkhorimoto, 2017/06/01 17:55:33]

Whoop, I think I accidentally reverted or something when trying to upload this. 
I uploaded an actual fix.

       [referencedFiles addObject:fileName];
     }
   }
@@ -748,7 +754,9 @@ - (BOOL)restoreSessionWindow:(SessionWindowIOS*)window
   BOOL closedNTPTab = NO;
   if (oldCount == 1) {
     Tab* tab = [self tabAtIndex:0];
-    if (tab.url == GURL(kChromeUINewTabURL)) {
+    BOOL hasPendingLoad =
+        tab.webState->GetNavigationManager()->GetPendingItem() != nullptr;
+    if (!hasPendingLoad && tab.lastCommittedURL == GURL(kChromeUINewTabURL)) {
       [self closeTab:tab];
       closedNTPTab = YES;
       oldCount = 0;