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 c08186dc5fd2f508c753ea99c448da51bb734eee..73284463194f123cf7aad8b8002d9e476b04dd3d 100644
--- a/ios/chrome/browser/tabs/tab_model.mm
+++ b/ios/chrome/browser/tabs/tab_model.mm
@@ -610,8 +610,9 @@ - (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& URL = tab.lastCommittedURL;
+    if (UrlIsExternalFileReference(URL)) {
+      NSString* fileName = base::SysUTF8ToNSString(URL.ExtractFileName());

[kkhorimoto, 2017/04/14 20:37:40]

A file is currently reference if it's in the content area, which would be the
last committed.

[Eugene But (OOO till 7-30), 2017/04/14 21:46:10]

Should we include both lastCommitted and pending?

[kkhorimoto, 2017/05/31 22:30:04]

Done.

       [referencedFiles addObject:fileName];
     }
   }
@@ -772,7 +773,7 @@ - (BOOL)restoreSessionWindow:(SessionWindowIOS*)window
   BOOL closedNTPTab = NO;
   if (oldCount == 1) {
     Tab* tab = [self tabAtIndex:0];
-    if (tab.url == GURL(kChromeUINewTabURL)) {
+    if (tab.lastCommittedURL == GURL(kChromeUINewTabURL)) {

[kkhorimoto, 2017/04/14 20:37:40]

Loads aren't occurring during session restoration, so last committed is
sufficient.

[sdefresne, 2017/04/18 15:54:34]

This is also called when restoring a session after a crash. There can be a
pending tab if the user started a navigation and then immediately tapped the
"Restore tabs" button from the infobar. I think we also need to check pending
here as we do not want to close the pending tab in that case.

[kkhorimoto, 2017/05/31 22:30:04]

Done.

       [self closeTab:tab];
       closedNTPTab = YES;
       oldCount = 0;